Conference vmszoo::rc

FM is generally accepted as better than AM for rejecting interference, the PCM
is said to be better again, however I believe the quality of construction of
the radio has to be looked at carefully. For example a cheap FM radio could
well be out performed by a good AM radio. 

RADIO SELECTION.

Decide what you want to do in RC during the next 4-5 years as you can expect
that length of service from the radio. Buy a radio that will give you the
number of channels you require, (I suggest 5-6 channels as normal); the
features (eg mixing, rate switches, roll buttons, etc.); and how much you are
prepared to spend (or your wife/girlfriend let you spend), and shop around for
the best deal. Watch the servos, the price of a radio will vary greatly 
depending on servo quality. A good servo can be 3 times the price of an 
average quality servo. The core less servos are the best but for general
sport flying an unnecessary expense, provided the servo is smooth and
accurate in operation it's all that a NORMAL SIZE sport models require. 

John

    waht will the 5th & 6th channel let me do ?
    
    (I can see 1 through 4 easily enough: elevator,rudder,throttle,
    ailerons)..

    
    HERE GOES NOTH'EN,
    
    	First of all don't buy less than a four channel radio if
    you are intending to use the radio for aircraft. I say this 
    because if you but say a three channel unit after you learn
    how to fly very rarely will you be using any less than four
    channels.
    	PCM, I doubt that you will be able to find any PCM unit
    that has less than six channels and costs under $ 250.00.
    Not what you would call a beginners radio. There great if you
    can afford it. Also you may wish to run a bigger flight pack
    battery (ie, 750 ma.) as the PCM seem to draw more power than
    a std. AM or FM radio.
    	I have heard that FM's have better rejection. Any good
    system properly maintained will work.  I don't think that the
    final chapter on the plus's and minus's of AM over FM has been
    written. 
    	For your first system buy the Manufacturer and mode that
    is similar to those that are used by the people you will be
    flying with. This familiarity(sp) will help you and the 
    instructor. this way you can directly draw on the knowledge that
    others around you have. After you have been in the hobby for
    a while you can get a better feel for what system is better
    suited for you. I myself now fly JR systems in my pattern
    birds because I think they are the best thing going. In my
    sport and scale ships I fly my Futaba systems because I have four
    systems from this manufacturer. 
    
    	If you were going to fly serious competition I would suggest
    that you buy a top of the line system from JR or Futaba.
    
    	If this is your first radio, again buy what is familiar(sp)
    and what you can locally get parts for. ie servo trays, batteries
    switches,servos.
    
    
    						Tom

    re .-1
    
    "properly maintained": does this imply that adjustements can be
    made between the receiver & transmitter (I know that my hi fi FM
    section drifts and I get it adjusted every other year)
    
    If adjustements are possible, do you have to get them done
    professionally or can this be done be me ?
    
    md

	re .-a couple



			5th and 6th channels would normally be used
	for retracts and flaps.....

	bob

On the subject of "properly maintained".  Yes, the job should be
done at a shop.  There are a couple of reasons for this.  One, its
illegal for anyone other than an FCC licensed tech to make
adjustments to the output stage of a transmitter.  Secondly, it does
take some good test equipment; a frequency counter, and good DVM
would be minimum, but the 1991 regulations will be forcing us to put
the transmitter on a spectrum analyser too.  At the last NATS the
AMA did a spectrum check on transmitters and found about 50% of them
to be out of tune.  Surprisingly, many new transmitters were badly
out of tune, too.  After you leave the RF circuits, however, the
only other adjustment that would cause interference would be the
output of the encoder, which may cause overmodulation.  In the
encoder itself, the time of the channel pulse must be set, but that
only needs a properly calibrated scope.  There are other adjustments
on the encoder, depending on the brand and complexity of the
transmitter that need to be made.  That's all for the conventional
AM and FM stuff; for PCM, all bets are off, since its largely
digital logic.  I wouldn't even trust a PCM to the average RC
technician!

For the receiver, its mainly a case of IF alignment; if your
transmitter is on freq, and you have an oscilloscope, you can do the
job as well as anyone.  

For reference, check out Fred Marks' book, Getting The Most From
Your Raido Control System...or something like that.  Its THE book on
the subject of RC electronics.  Doesn't talk about PCM, though.

Why do you need a 5th and subsequent channels. Let your imagination run wild 
and have some fun. As said in previous notes retracts and flaps are common, I 
always use an inflight mixture control even on a four stroke. You don't have to 
worry about holes for the needle valve and it is a little safer than putting your 
fingers near the prop to adjust the mixture. Have you thought about Bob Drops 
Air Brakes or Smoke Systems in your scale projects, they could all use an extra 
channel. If you make a twin powered model a differential for the throttle is a 
good idea the list goes on, I can assure you 6 channels can easily be used.

As to proper maintenance. Regular checking by a qualified technician is very
important, however, you should regularly check the antenna, servo leads, switch
harness, plugs etc for damage or deterioration. Cycle the battery regularly to
ensure it is not loosing capacity, ensure the radio packing is not deteriorating
and the Rx getting soaked in oil from the fuel etc. Next check the model to
ensure the control surfaces are not too tight or to loose. If they are tight
you load the servos, if they are loose the vibration can damage the servo gear
train. Check/clean the Tx antenna, oil from your hands will detract from the 
effectiveness of its radiation. 15mins checking the equipment in this way will
help prolong the life and reliability of your radio equipment. 

We have slightly different frequency management in Australia, we are allowed 
more freedom to modify our equipment. I use a Glass CB type of antenna on my 
Futaba radios, it is center loaded to improve the radiation, and I never have 
to worry about dirt in the joints. The big disadvantage is you always have to 
carry around a 3' long glass rod. If you want a little extra insurance and it 
is permissible under your regulations its a worth while mod.

John.

re: -1: Never really thought about it; but are you folks on the
European frequencies.  That's the 35 MHz band isn't it?  How's the
interference problems from each other and other services?  Golly,
is anyone besides the US on 72 MHz?

<    Re: -1. We do have some interference problems mainly with the DUM
    (present readers excepted) Buggy owners who think as you use a
    different radio there is not a problem. The odd CB, Radio/TV Station,
    and Pager System are a minor problem. We don't have the interaction
    problems you guys have, I don't remember the details but when I was
    at the 85 NATS at Chicopee I recall that Pattern and Chopper had
    major difficulties and had to change the matrix.
    
    In Australia we have bands on:-
    
    27mhz about 15 slots. Used in the Bush but no good in the metro area.
          Too many CB's.
    40mhz 3 slots 2 of which are ok to use the other is close to a pager
          frequency.
    29mhz 12 slots. Used by RC Aircraft, Boats and Cars.
    36mhz 16 slots. Restricted to Aircraft and Boats only. Radio must
          have 16kc band width or better. We actually used this band
          in the US in 85 and it was very clean. (we had special permission
          for the World Champs.)

    If you come to Australia don't ever use 72mhz, we have TV stations
    on that frequency. I tried to set up a model on the bench using 72mhz 
    modules and gave up because of the noise. We are applying for a
    section of the 800mhz band for future use (probably +10 years).
    This is more to show we are planning ahead to the Dept. of
    communications than a need at this time. The 35mhz band is not used
    officially but we are trying to get it.

    John.

    I called FUTABA the other day. They are sending a pile of stuff.
    I will keep you posted on what I get. 
    
    BTW, the lady mentioned something interesting: Depending on local
    conditions, pick AM or FM. Sez to check (talk to other RCers for what 
    works well).   Any one care to comment ??
    
     PCM is different (not sure what she ment)

    I got the stuff from FUTABA. It consist of 3 fliers: a glossy that
    lists their complete product line (2 pages). includes list prices.
    
    a flier that gives full size templates of all servos & receivers
    (4 pages)
    
    a flier that list all accessories available (4 pages)
    
    any one interested: send me mail & tell me what you wnat and where
    to send it.
    
    md

    Boy, it's been a while since anyone has hit this note, but I think it's
    worth a new discussion.
    
    I just sold my Pussycat and WE Expert 7 channel FM as a package to a
    neighbor (also offered to teach him to fly... the blind leading the
    blind!).  I have another sailplane (100", probably a Graupner ASW22,
    I'm not sure, neither was the seller!), but I need to get a radio.  I
    plan on buying it at the MARC show in Baltimore this weekend, there are
    usually some great deals from the major mail-order houses.
    
    I have some questions.  I just went through a large catalog (RCM!) and
    am bewildered by several things.
    
    1) AM 1991 radios?  I thought you needed FM or PCM.  
    2) Which mode is better & why? AM, FM, PCM.  Strengths/weaknesses.
    3) Staying with major brands, is there a better or worse?  No biases,
    just real-world reasons.
    4) Aristo-Challenger, made by Hi-Tec, I know, but are the servos crap?
    Seems to me I heard that, but the WE 7 channel was great.  BTW, last
    year at the MARC show I had the WE checked at the AMA booth.  The guy
    saw it and said,"We'll check it, but there's no need to, we've NEVER
    had one fail 1991."  Needless to say, it wore a gold sticker home!.
    
    This is a discussion I don't think has taken place since the bulk of
    the 1991 systems have surfaced; it's due.
    
    Thanks in advance for a lively discussion!
                             |                      
   \	       	         ____|____                      /   Regards,
    \________________________O_________________________/    Frank.
    

    From what I've read and understand at this point. The ONLY thing
    that you should buy if you plan to keep the radio is a unit that
    comes with a "DUAL CONVERSION REVEIVER". Anything less in the future
    will enhance the possibility that you "might" get hit. Seems that
    most of the companies offer this. Some offer this presently only
    in more expensive radios. Airtronics offers this in their cheap
    Vangard series. (PS: I own all FUTUBA). PCM as written in previous
    notes has it's advantages with no disadvantages that I know about
    other than higher cost. You need to decide what you want to spend,
    how long you "think" you will keep the radio, how much functionality
    you want or may need, and how much extra protection from interferance
    your need to be concerned about. All this relates directly to $$$.
    
    I personally will buy nothing but PCM after having been shot down.
    the extra $100 bucks for the PCM has already paid itself back. In
    this case without PCM and it's failsafe my ship would have been
    history.
    
    
    
    						Dave
    

    We're talking strickly sailplanes,Right?
    
    
    OK, If it were me I'd buy the Airtronics in FM or if available I'd
    go all the way and get the PCM. Airtronics is the only manufacturer
    to date that sells a system designed exclusively for sailplanes.
    I understand that the system gives you some added flexability and
    mixing of channels that is different from other sets. 
    
    Understand that AM and FM are modulation types. PCM is a coded
    bionary signal specific to the system your operating. To date I
    haven't seen a PCM system on any other modulation other than FM.
    
    I myself prefer JR systems. I just do. However if I were to get
    serious about sailplanes I'd probably give the Airtronics system
    a serious look. If after that I didn't buy the Airtronics I'd
    probably opt for a JR PCM10 aircraft system and control a number
    of sailplanes from the same transmitter.
    
    
    Tom

    re: .15
    
    Regarding the Sailplane radio by Airtronics. This Radio is the MD7SP
    and yes all of the mixing has Sailplanes involved.  Spoilerons,
    Flaperons, Spoiler on the Throttle stick/mixed with elevator, Elevator
    Presets (launch, normal, cruise)  This is just a standard FM tx with a
    DUAL CONVERSION Rx.  The next up the line is the VS8SP(?) which is the
    VISION system that has the ATRACS module in it that will basically let
    you do everything the PCM 1024 and the JR10's will do.  All computer
    controlled, lets you do anything with anything, FM modulation with
    either PCM or PPM selectable depending on the Rx (I think it comes with
    standard Rx that is by default PPM? not sure).  And the whole box is
    engineered around Sailplanes.  Also lets you store multiple
    configurations for different planes.
    

re Note 51.16      The MD7SP and VS8SP by Airtronics 
    
    On the advice of Kay I went shopping (well, window shopping maybe)
    for these two radios for my first of perhaps many gliders.  Neither
    Tom's or the place near Spit Brook carry Airtronics.  Both said
    that they were unable to get reasonable service on parts.
    
    1.	Is that a generic problem with Airtronics?
    
    2.	Where can I get literature on these products, short of writing
    	a letter?
    
    3.	Where can I get them for reasonable prices?  The mail-order
    	people seem to focus on the VG series, not the VS.
    
    4.	Since I am a beginner/crasher, should I buy a used unit?
    
    Alton, who has a new Gentle Lady in the box.  

>    On the advice of Kay I went shopping (well, window shopping maybe)
>    for these two radios for my first of perhaps many gliders.  Neither
>    Tom's or the place near Spit Brook carry Airtronics.  Both said
>    that they were unable to get reasonable service on parts.
>    
>    1.	Is that a generic problem with Airtronics?

No - I'll bet you didn't see any JR radios either.
Incidentally as of the latest AMA magazine JR now has radios that
have been certified as meeting AMA guidelines.

So the only AMA guideline certified radios are Airtronics and some JR.

In the East coast most hobby shops carry Futaba and the world engines
expert stuff (I think).

I believe that on the west coast many hobby shops carry Airtronics.

I have replace an Airtronics servo (in a RC Car) by having my local
hobby shop order one - came in very quickly.
    
>    2.	Where can I get literature on these products, short of writing
>    	a letter?

Try a magazine.  All the leading vendors have full page glossy ads.
The latest RCM has full page ads describing the Airtronics Vision.

>    3.	Where can I get them for reasonable prices?  The mail-order
>    	people seem to focus on the VG series, not the VS.

Tower and Sheldons both advertise and sell Airtronics MD7SPs and Visions.
    
>    4.	Since I am a beginner/crasher, should I buy a used unit?

No.
Get a NEW "certified as meeting AMA guidelines" 1991.    

>    Alton, who has a new Gentle Lady in the box.  

We could start a separate note about the Lady that Al keeps in a box.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
================================================================================

    re .17..
    
    get the number out of an rc mag for airtronics....they'll send you
    a brochure on their line of radios. 
    (i've got one somewhere...if i can find it i'll send it to you.)
    
    

    I have used only Airtronics. They are readily available via mail
    order, as has been stated. Tower Hobbies carries a full line of
    replacement parts, down to servo repair parts, and all types of
    servos. Sheldon Hobbies usually has the best prices for complete
    radio sets.

    Airtronics servos and repair parts are cheaper than Futaba.
    I don't know why local hobby shops don't carry Airtronics, maybe
    there is less of a mark up or something. I'm all for supporting
    my local hobby shop, but if they don't carry what I want I think
    it's better to tell them and then order it by mail.

    I have called their California office several times and they
    are very friendly. Their technical guy (his name is Jack) is
    very helpful, and they do repairs and conversion there. Jack
    even sent one of us a schematic of the radio. They've done ham
    conversions for me for free (on new radios, you pay shipping both
    ways). Don't try to buy stuff directly from Airtronics - they
    charge full list price and you can get it for almost half that
    from mail order houses.

    Dave
    

I've got another "money spending" request.

I was at a friend's this weekend and he asked me if I had been flying recently.
(we used to fly together in college and then lost touch) I said that I needed 
batteries for my old Kraft gear and 1991 and... Anyway he gave me the current 
Tower Talk and pointed out the Futaba 4ch Attack for ~$100 so...

I know I've read about people waiting for Attacks to arrive, are the owner's
happy with them? This is at the top end of "getting active again" if I were to
try for anything more expensive I'd be told to "just buy the batteries".
I know about the problems with channel 20 and TV4 (Boston area), are there any
other "bad" channels?

I figure I can always use the 4ch in gliders and the 3&4ch sport stuff I 
generally fly and I'll probably get Futaba gear if I get into it bigtime again
so the servos will be compatible...

The standard servos don't bother me for now since my planes are all set up for
a tray of fullsize Kraft ones anyway...

Any other pros and cons I've missed??

    Does anyone in the northeast have a list of potential 72 mHz
    interference sources, a table with the following data?
    
    	assigned frequency
    
    	allowed power
    
    	antenna location
    
    	use (e.g. pager)
    
    	organization name
    
    Just to be greedy, I'd like it in computer-readable form. With a list
    like this and a list of frequencies used by our fellow club members,
    we'd be in a better position to decide on the channel of our next radio. 

>I didn't mean to restart the religious war (well maybe I did ;^) but I'm faced 

Can you tell - I like arguments about religion?

>I like the idea of failsafe mode but what does PCM buy you on top of these 
>features and what else should be considered?

Nothing - I've got a conceptual bone to pick with PCM.
More later in this note.

>I've looked at additional flight packs vs total systems and don't want to 
>have to "upgrade" to a better Rx at the "whole system" price. 

Historically only the previous owners of Airtronics radios have escaped
the marketers on this one.  And then only in the case of the 1991 upgrade.

>Do I really have to buy top of the line in order to feel safe? 

Absolutely not.  Think Airtronics FM dual conversion (Vanguard).

>What about these "problems" with the Futaba 1024 systems. I hate the idea
>of buying something that hasn't been proven in the (pun alert) field for a 
>reasonable amount of time. 

By all accounts Futaba has fixed any problems they had with the 1024 systems.

>Do I just merrily go on with my AM Attack until I get shot down real hard?

Well - that's up to you.  If your careful and watch for channel 20 and dirt
bikes - you can probably survive.  If I were you I would just leave the 
Attack alone and only worry about a new radio in your next new plane - you
are building a new plane this winter aren't you?

>A few weeks ago I got hit (radio interference) with a dirt bike that was acting
>(I assume) as a spark Tx. Will any of these systems/features tolerate this type
>of hit better (besides just throwing up its hands and going to failsafe mode)? 

Sure - all FM and FM/PCM systems should hold up against this kind of noise.
They always have in the past.

Not about my bone to pick with PCM.
First let me say that most experts disagree with me on this point.
Never the less...

Suppose you have this neat noise generator with a big knob on the front
and a dial indicator such that you can crank it up to any level of noise.
Further you have a half dozen types of noise you can generate.

I maintain that if you placed two planes out on the runway and had two
transmitters some distance away - say 100 yards.  Assume that these are
all separate tests such that the two radios are never turned on at the same
time.  

Now you set at your bench with your noise generator - say 1000 yards from
the radio sets.  You turn up the dial on your noise generator until the
receiver looses the signal from the intended transmitter (fail safes in
the case of a PCM).

I maintain that a FM/PCM radio will fail before a plain vanilla FM.
This is because I believe the packets transmitted will start to fail
checksum and the PCM radio will start rejecting the signal while the
FM set will maybe jitter a servo occasionally and keep accepting data.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
================================================================================

I don't know if pcm does a checksum; I thought it was a
comparison with the previous frame for sanity???  George Meyers
in MA and Bob Aberle in FM are always trying new tests -- I bet
they'd be interested in hearing of your test, and I'd bet they'd
try it too!

I'm still hot for the Airtronics PCM Vanguard.  At $239 mail
order I think its the best bargain going.  

Please don't blast the AMA too hard, poor dear souls had this
frequency thing shoved down their throats, and they're making the
best of it.  But when they tell me I've got clear channels now --
when the fact is that they're only clear on paper, I do get a
little riled too.

RE:  <<< Note 105.151 by K::FISHER "Stop and Smell the Balsa!" >>>

> Now about my bone to pick with PCM.
> First let me say that most experts disagree with me on this point.
> Never the less...

Well, I'm no "expert", but I do understand enough about PCM to know
where you're going wrong here.  Hopefully, I'll be able to convince you.

> Suppose you have this neat noise generator with a big knob on the front
>       ....
> I maintain that a FM/PCM radio will fail before a plain vanilla FM.
> This is because I believe the packets transmitted will start to fail
> checksum and the PCM radio will start rejecting the signal while the
> FM set will maybe jitter a servo occasionally and keep accepting data.

Here's why your theory is wrong.  In an attempt to explain myself over
the "tube" I'll have to make up a way to talk about it.

To make matters simple, let's talk about just one channel - how about
"elevator".  Now, I'm going to assign a number to each of the possible
stick positions.  For example, pulling the stick all the way back (Full
up elevator) will equal 100.  With the stick all the forward (full down
elevator) will equal 0.  So, neutral elevator will equal 50.  For every
position in between, there is a number that is proportional to the
relative position from full down elevator.

So let's say you're flying your Panic and doing all kinds of wild
aerobatics that only Panics can do.  For an time span of 1/2 second, you
push the stick to full down and then pull it back for full up then
return to neutral to relax.  The numbers corresponding to your elevator
stick position are:

    50    start at neutral
    10    almost full "down"
     0    full "down" elevator
    45    almost neutral (slightly down)
    50    return to neutral
    75    half way between neutral and full up
   100    full "up" elevator
    70    nearly half way between neutral and full up
    50    return to neutral
    50
    50      (relax)
    50

Normally, both FM and PCM will receive the electronic codings of these
numbers correctly and tell the servos to do the correct thing. 

Now, if we add your noise generator, both FM and PCM will begin to get
some of the numbers wrong.  However, what each receiver does with them
is different.  Let's say these are the numbers that each receiver
"thinks" it received:  ("***" indicates error)

    50    start at neutral
*** 90    almost full "up"  ***
     0    full "down" elevator
*** 87    almost full "up"  ***
***100    full "up"         ***
    75    half way between neutral and full up
   100    full "up" elevator
    70    nearly half way between neutral and full up
    50    return to neutral
***  0    full "down"       ***
***  0    full "down"       ***
    50

Here's how each receiver and decoder deals with this


RF says     FM decoder          PCM decoder 
            tells servos        tells servos

    50        50                    50
*** 90        90 (glitch)           50 (bad checksum - hold last value)
     0         0                     0      (Good checksum - update servo)
*** 87        87 (glitch)            0 (bad checksum - hold last value)
***100       100 (glitch)            0 (bad checksum - hold last value)
    75        75                    75      (Good checksum - update servo)
   100       100                   100
    70        70                    70
    50        50                    50
***  0         0 (glitch)           50 (bad checksum - hold last value)
***  0         0 (glitch)           50 (bad checksum - hold last value)
    50        50                    50      (Good checksum - update servo)


So, you can see that the PCM decoder will hold the last good value (last
frame with a good checksum) instead of updating the servos with random
garbage.  This is best illustrated in the last 4 lines of my example. 
If you think about how you fly, you don't normally go full down elevator
to full up elevator back to neutral in 1/2 second unless you're flying a
Panic.  Typically, in a period of 1/50 second (the typical frame rate),
you move the stick very little and the numbers don't change all that
much.  In reality a typical sequence of numbers would look more like:

    50 51 51 51 52 53 53 54 55 55 55 56 55 54 53 52 51 50 50 50 50 50 

Thus, it is usually best to hold the last known good value instead of
giving the servos a garbage number.

In addition, if the PCM decoder gets _ALL_ of the frames in one second
as garbage, it will preset the servos to the failsafe position.  The FM
decoder will just glitch the servos all over and crash your plane.

I've gotta' go...  Is this as clear as mud?

                       _____
                      |     \
                      |      \                          Silent POWER!
      _        ___________    _________   |            Happy Landings!
     | \      |           |  |         |  |
     |--------|-  SANYO  + ]-|  ASTRO  |--|              - Dan Miner
     |_/      |___________|  |_________|  |
                      |       /           |     " The Earth needs more OZONE,
                      |      /                       not Caster Oil!! "    
                      |_____/

Re: .154 - Evil Eric  ;^)

Point 1. My "tout" reference was to the description of the "Panic" radio system
	on one of the last few DECRCM videos. Should I have said that you were
	"enthralled"? You do a good selling job but I wanted some facts too ;^)

BTW I feel that this is a GREAT discussion and I hope it can be keyworded or 
extracted to be found by the next novice trying to figure out where to spend 
his money.

Point/question 2 is why do you feel safer with a PCM in the case of another
Tx on the same freq? Is it because you feel that you'll pop into failsafe
until he switches off? I hope you aren't screaming towards the ground with 
your Panic at the time. Though, I must admit that any kind of a hit at a 
time like that would likely be fatal.

Question 3 How'd you test your failsafe settings? Switch off while in a 
reasonable altitude/attitude/position?

I'll go home and look up the info I have on the Airtronics Vanguard PCM. $239 is
certainly in the cost range I'm looking. I'll need 5 channels for my Panic ;^)

>So, you can see that the PCM decoder will hold the last good value (last
>frame with a good checksum) instead of updating the servos with random
>garbage.  This is best illustrated in the last 4 lines of my example. 

I wish it were so.  Maybe it is but unless one of us can see better
specifications or get a look at their micro code we can only guess.

My understanding is that the frame with good checksum represent all the
channels in one packet - not just one channel.

So imagine you are flying along with fairly modest stick movements and
transmitting 9 channels worth of info - it would look like this.
            ID   Elev Ail  Thro Rud  Flap Bomb Ret  Misc Misc Checksome
Frame   1:  13   50   51   51   51   52   05   90   53   54   163
Now you make small corrections and several times a second new packets look
like this:
Frame   2:  13   50   52   51   51   52   05   90   53   54   164
Frame   3:  13   51   53   51   51   52   05   90   53   54   166
Frame   4:  13   52   54   51   51   52   05   90   53   54   168
Frame   5:  13   53   54   51   51   52   05   90   53   54   168
Frame   6:  13   52   54   51   51   52   05   90   53   54   167
Frame   7:  13   51   54   51   51   52   05   90   53   54   166
Frame   8:  13   50   53   51   51   52   05   90   53   54   164
Then the unspeakable happens
Frame   8:  13   50   53   51   51   52   05   90   38   54   164
                                                    ^^
Noise on channel 9 (which happens to be unused) so the check sum is
wrong.  Note that I just dropped the 5 bit (value 16).  A lousy 1 bit error.

So if you keep getting noise (no matter where) after 2 seconds (or so)
the PCM radio failsafes.

What would an FM signal do in this same environment?

Well - there are no bits to drop - perhaps the signal would get a
little distorted:

Demodulated FM signal before noise:
   +-+       +-+       +-+      +-+     +-+      +-+      +-+   +-+     +-+    
   | |       | |       | |      | |     | |      | |      | |   | |     | |    
   | |       | |       | |      | |     | |      | |      | |   | |     | |    
   | |       | |       | |      | |     | |      | |      | |   | |     | |    
---+ +-------+ +-------+ +------+ +-----+ +------+ +------+ +---+ +-----+ -----

==============================================================================
Demodulated FM signal during noise:
   +-+       +-+       +-+      +-+     +-+      +--+     +-+   +-+     +-+    
   | |       | |       | |      | |     | |      |  |     | |   | |     | |    
   | |       | |       | |      | |     | |      |  |     | |   | |     | |    
   | |       | |       | |      | |     | |      |  |     | |   | |     | |    
---+ +-------+ +-------+ +------+ +-----+ +------+  +-----+ +---+ +-----+ -----
                                                    ^ Plus longer than normal
FM ignores this noise.
==============================================================================
Another kind of noise:
   +-+       +-+       +-+      +-+     +-+     +--+      +-+   +-+     +-+    
   | |       | |       | |      | |     | |     |  |      | |   | |     | |    
   | |       | |       | |      | |     | |     |  |      | |   | |     | |    
   | |       | |       | |      | |     | |     |  |      | |   | |     | |    
---+ +-------+ +-------+ +------+ +-----+ +-----+  +------+ +---+ +-----+ -----
                                                ^ Pulse starts too early
FM glitches one channel a little (ah - but it is an unused channel)

==============================================================================
   +-+       +-+       +-+      +-+     +-+               +-+   +-+     +-+    
   | |       | |       | |      | |     | |               | |   | |     | |    
   | |       | |       | |      | |     | |               | |   | |     | |    
   | |       | |       | |      | |     | |               | |   | |     | |    
---+ +-------+ +-------+ +------+ +-----+ +---------------+ +---+ +-----+ -----
                                                 ^ Pulse is missing
FM keeps servo at last known position


==============================================================================
   +-+       +-+       +-+      +-+     +-+      +-+      +-+   +-+     +-+    
   | |       | |       | |      | |     | |      | |      | |   | |     | |    
   | |       | |       | |      | |     | |      | |      | |   | |     | |    
   | |       | |       | |      | |     | |      | |      | |   | |     | |    
---+ +-------+ +-------+ +------+ +-----+ +------+ +------+ +---+ +-----+ -----
FM pilot must land now to help the FM/PCM pilot look for airplane parts!

Bye          --+--
Kay R. Fisher  |
---------------O---------------
================================================================================

    RE: .157
    >>So, you can see that the PCM decoder will hold the last good value (last
>>frame with a good checksum) instead of updating the servos with random
>>garbage.  This is best illustrated in the last 4 lines of my example. 

>I wish it were so.  Maybe it is but unless one of us can see better
>specifications or get a look at their micro code we can only guess.

According to a series of articles written in the now defunct Radio Controlled
Helicopters, Eric's description of what happens is correct for the
JR PCM 9 radio and probably others as well. To quote:

	"the signal is then checked for acceptability and if OK is
	 then passed to the 9 bit data channel and converted to the
	 normal 1 to 2 msec pulse that a servo understands. At the
	 same time this acceptable signal is supplied to the memory
	 (RAM) for temporary storage untill the next incomming acceptable
	 signal. The reason for this is that if a corrupted signal
	 arrives it will be rejected and the RAM will be instructed
	 to supply the latest good signal to the data channel."

>My understanding is that the frame with good checksum represent all the
>channels in one packet - not just one channel.

The same article mentions that there are numerous ways of doing error
correction but the simplified PCM frame they show does agree with Kay.
They show a 24 bit checksum for all of the channels.

Now for my 2 cents. I agree with Eric about PCM. For a fixed wing flyer
I don't think you can do better. You may still get clobbered but at least
you've made every effort to save your plane before it left the ground. I've
flown with nothing but my two JR Century VII's for the past four years. I 
wouldn't dream of flying a helicopter with AM. But even with FM I've still 
been hit by things like farm tractor ignitions or loose metal on the copter.
The only reason I'm luke warm about PCM on copters is that while keeping
the last transmitted value is definitely better than driving the servo past
its limits, its still not the correct value. Things go wrong so quickly
that anything but the correct value may still put the copter in the ground. 

Kay Fisher, I've found an out for you. Check out page 158 of the November
RCM. It conttains part of an article by Ray Hostetler comparing the
JR PCM 10 and Galaxy Helicopter radios. Ray mentions that there's a 
growing debate as to whether FM or PCM modulation is better. Some say they
can feel the difference. 8^)

Also from the same RCM on page 132 is an add for Sheldon's Hobbies new
'bullet proof' replacement reciever. It looks impressive and the 
introductory price of $60 sure can't be beat. (Usual diclaimers) Any
comments?

Dna Eaton

    re   the bit pattern used for frame verification
    
    This _might_ be a checksum (i.e. an operation performed on all the
    characters to detect almost any flaw in any of the set of characters),
    or it _might_ be a synch character (i.e. a designed-in, known character
    that must be present and uncorrupted in every frame).
    
    I do not know which it is; I haven't asked a manufacturer.  Next
    time I call Airtronics, I shall ask.  
    
    Either could work for the purpose of frame fault-detection.  Either
    could work for the unrelated but important purpose of frame demarcation. 
    The synch character approach is probably less expensive to implement,
    and if the failure mode tends to be a [relatively long] burst of
    total corruption, the synch approach is quite sufficient.
    
    Who cares?  Well, this obscure point has a bearing on Kay's conjectures.
    
    And it leads me to predict that by 1997 all of our radios will be using 
    both spread spectrum and error correction techniques.  The technologies 
    are trivial, well known, not new, and getting less expensive.  Frequency 
    synthesis will lay some of the groundwork and will be needed much sooner.
    

    Everybody (Kay) that is disagreing with both the explanation that both
    Eric and Dan M presented has two things in common. One they don't own
    a PCM radio, and two, they just think they know how they work. To hell
    with your theories. Buy a PCM and see how it works seeing that you only
    think that you know.  I was the person who in fact was able to
    catagorize the channel 20 problem. I have 2 PCM's radios. The one that
    got hit by channel 20 was a single conversion Futaba PCM. I can assure
    you that the servos react to interferance EXACTLY how Dan Miner has
    explained. (They hold last posistion on bad data, and they immediatly
    jump to the new position correlating to the stick position when a
    good data packet gets through) So you have control. Why did I know I
    had been hit by chan 20 and not have an equipment failure. BECAUSE
    I had PCM. The throttle went into failsafe, and even though stick
    movements resulted in very delayed servo response, I SAFELY landed the
    plane while chan 20 was still active. I then put the pane up several
    times and had the owner of the chan 20 radio turn it on while I was
    40 feet up or so. IN ALL cases, I kept control of the plane though it
    was quite sloppy as one tends to give it more stick when nothing
    happens. 
    
     You can state what you want, and you can believe what you want to
    about PCM. But please don't try to tell a PCM owner how you think
    it works when your wrong. I will not argue subtle points about how
    the RX works internally as I do not know. I only know what I see
    and I have seen mine work as Dan M and Eric has described.
    
    
    						Dave
    

< Note 105.160 by CSTEAM::HENDERSON "Compete fairly, and still win." >
    
>    You fly your bi-plane and I'll fly mine. Arrange for a TX to be
>    turned on that is on your frequency and for one to be turned on
>    that is on mine. We will both start at three mistakes high. See who
>    stays up the longest before one of us has to ask their offending TX
>    to turn off.

Some of the more foolish souls of my generation used to play this
game with cars: it was called "Chicken".

Thanks for the discussion guys, I just quanity squared my
knowledge of PCM!    

    
    
    Kay is correct that a vanilla FM set would probably be better than
    FM/PCM for the disturbance he described, i.e. tiny glitches at
    properly spaced intervals.  You can definitely come up with certain
    interference patterns that will make an FM/PCM failsafe to the ground
    while a vanilla FM would fly with small glitches.
    
                            --- HOWEVER ---
    
    I personally think that the probability of Kay's type of interference
    compared with the kind that favors PCM is slim to none.  3IM or
    someone switching onto your channel are the dominant sources of
    interference.  I'd rather go failsafe than "glitchy".  I've had
    a short burst of 3IM kill my Citabria because it was low in final
    approach.  Failsafe would have saved it from significant damage.
    
    Bill
    
    

>    Theory, theory, theory...try some reality!
>    
>    Take the Pepsi challege Kay.
>    
>    You fly your bi-plane and I'll fly mine. Arrange for a TX to be
>    turned on that is on your frequency and for one to be turned on
>    that is on mine. We will both start at three mistakes high. See who
>    stays up the longest before one of us has to ask their offending TX
>    to turn off.

I think I did.  If you read the weekend notes 771.* earlier this year
I was flying my Aeromaster when Dwight Aube(sp) decided to tune up the
engine on his Ducted fan.  I didn't yell "I'm getting hit"  I just
got several unexplained glitches.  I took one more lap and got some more
hits.  Then I told Kevin that I didn't know what was wrong but I was
landing.  I made a normal landing (all but long and had to take a long
walk down the runway.  I had convinced myself that my Rx battery must
have gone bad but when I returned with my plane Dwight came up to me
and apologized that he had misread a frequency pin and had his channel
38 transmitter on.

What does this prove - nothing!

I never said that FM was BETTER than PCM - never.
What I said was that the PCM concept is a little scary in that it can
decide to reject packets when one bit is bad!  One bit!

>    I do not like the Lock-where-were-and-low-throttle failsafe option
>    because it does not warn you soon enough that you are in trouble.
>    But that is just a personal pref.

Some PCM receivers automatically have throttle failsafe.
That is a scary concept when you apply it to sailplanes.
Can't think of a channel I want taken to the limit while
failsafing on the winch.  Assuming the throttle channel is hooked
to spoilers or flaps - I sure don't want full flaps or spoilers
deployed on winch!
    
>    planes daily. I will continue to dog you as long as you demonstrated
>    that you do not understand PCM and continue to cloud the issues
>    for people who just ask for facts about what radio etc.

Precisely what about PCM have I demonstrated that I do not understand?
I'm sorry if I clouded the issue.  In case a prospective new radio
buyer is listening now - hear this.  PCM is wonderful.  It's great!
It's also expensive.

PCM doesn't always imply failsafe.  What hearsay?  The best sailplane
radio in the world has PCM but not failsafe (Airtronics Vision SP).

But in case I'm clouding some more - hear this.  Failsafe is wonderful.  
It's great!  It's also expensive.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################
    
    

I started this by asking about radio features for a future purchase decision and 
notice that Al Casey hasn't jumped in. Am I to assume that because Futaba got 
eliminated earlier that I/we won't benefit from his comments??

I've Got an Attack so I was upset that I couldn't consider Futaba J connector
compatible equipment as a migration path (Dual conversion requirement)

Also I noticed the ads in the Sept. RCM for the World Engines Expert but it 
doesn't STATE dual conversion Rx. I really liked my WE Blue Max in the 70's.
The new World Engines Expert seems pretty loaded even with PCM for <$300 but
"is it dual conversion?"

    I will be making a radio purchase in a week or so. It will be the
    Airtronics Vangard VG6DR FM PCM. My basic reasons for making this
    selection is as follows:
    
    	1. I already own a Vangard 4 channel FM system. I wanted to
    	   keep the compatibility. If I want to switch radio's between
    	   planes, all I have to switch is the receiver.
    
    	2. PCM technology and reliability. Given the current discussion,
    	   I won't say that I think it less prone to getting hit.
    
    	3. Fail safe feature. Say what you want about going into fail
    	   safe when your inverted, or in a dive or spin. I'd rather
    	   have it then not have it.
    
    	4. Low battery warning's on both TX and RX. The TX will beep
    	   at ya, and the receiver will cause the engine to throttle
    	   up and down on low RX battery voltage. I believe this is
    	   overridden on the next throttle command received. At any
    	   rate, it is overridden so you don't have to try and land
    	   with the engine reving up and down.
    
    	5. A couple of other little bells and whistles I can't think
    	   of right now.
    
    	6. An electrical engineer type person I know bought one and
    	   took it appart. He likes the way it's built, meaning it's
    	   better than it has to be for what it does. He was basicall
    	   very impressed.
    
    	7. I'm sure I could think of some other reasons, but suffice
    	   it to say that this just boils down to my personal choice.
    
    steve

    Jim,
    
    I haven't jumped in here for one simple reason: I'm not very
    technologically oriented, nor do I really want to be.  My knowledge of
    radio technology starts and stops with, "if it don't work, IT'S BROKE!"
    
    The only thing I can comment on, technically, is that the new Futaba
    1024's share most, if not all, of the features of other programmable
    PCM radios and I've found my new 7UAP to be extremely user friendly; if
    you can set up yer' digital watch, you'll have little difficulty
    understanding/setting up a 1024.  The other thing is that ALL PCM's (to
    my understanding) use the 5-bit microprocessor developed by Futaba when
    it introduced PCM a few years back.  ALL, that is, EXCEPT for Futaba
    themselves who have upgraded to a 10-bit microprocessor  (hence the
    "10"24).  Eric has commented that PCM's are not quite as smooth to the
    "feel" as conventionally modulated systems due to the 5-bit
    microprocessor.  This is precisely the reason Futaba went to the
    [exclusive for the time being] 10-bit; it's the next natural step in
    the progression of the state-of-the-art.
    
    I sincerely believe that it'd be difficult NOT to get a good radio by
    purchasing a PCM, dual-conversion system from any of the major
    manufacturers.  Like yourself, I already had scads of Futaba servos and
    other components so it behooved me to stick with them.  Suffice it to
    say that, after dozens of flights on my 7UAP (in the ol' Yeller'
    Peril), I'm ultimately satisfied with the system, its performance and
    user friendliness...I do not hesitate to recommend it highly.
    
    As with anything else, there are things I'd prefer to see done
    differently, e.g. I wish the Tx had conventional slide-switches on
    the 2-aux channels rather than the [pattern-dictated] rotary knobs but,
    by-and-large, I have very few, very minor nits about the ergonomics of
    the radio, and these are from a scale flyer's point-of-view...likely,
    a sport or pattern pilot would feel just the opposite about these nits.
    
    I don't know what else to add; Futaba is a _good_, 1991 approved radio,
    arguably a bit ahead of other makes, technologically.  But virtually
    any of the other radios touted herein are good reliable systems as
    well.  You simply have to select what makes the best sense for _you_.

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

>< Note 105.161 by TARKIN::HARTWELL "Dave Hartwell" >
>                -< Experiance beats the hell out of Conjecture >-
>
>    Everybody (Kay) that is disagreing with both the explanation that both
>    Eric and Dan M presented has two things in common. One they don't own
>    a PCM radio, and two, they just think they know how they work. To hell
>    with your theories. Buy a PCM and see how it works seeing that you only
>    think that you know.  

Boy - tuff crowd.  Dave your mother wears combat boots.
Now we're even.

OK - I have attempted to resolve the two things in common.  I just
called Sheldons and ordered 3 radios.  Actually 1 transmitter (a vision)
and 3 receivers.  1 PCM and 2 vanilla FM.  I would have ordered 3 PCM
if (1) they were not double the cost of non-PCM and (2) I believed in
PCM being the greatest thing since sliced white bread.  I would have ordered
all FM non-PCM but the marketers won't let me - one comes with the
vision and I have to pay for it.  OK now I own one and I think I know how 
it works.

By the way - I think I don't disagree at all with Eric and/or Dan about
the theory except for some minor technical details.  I've been at Orange
watching Charley Nelson turn his transmitter off while his beautiful WACO
makes gentle slow turns on failsafe.

>	I was the person who in fact was able to
>    catagorize the channel 20 problem. I have 2 PCM's radios. The one that
>    got hit by channel 20 was a single conversion Futaba PCM. I can assure
>    you that the servos react to interferance EXACTLY how Dan Miner has
>    explained. (They hold last posistion on bad data, and they immediatly
>    jump to the new position correlating to the stick position when a
>    good data packet gets through) So you have control. 

That's not what Dan Minor said - he said that only one channel might be
affected.  I disagree that the implementation does not have single channel
resolution and failsafe happens when any noise on any channel (even the
unused ones) causes a bad checksum.

>     You can state what you want, and you can believe what you want to
>    about PCM. But please don't try to tell a PCM owner how you think
>    it works when your wrong. I will not argue subtle points about how
>    the RX works internally as I do not know. I only know what I see
>    and I have seen mine work as Dan M and Eric has described.

Dave - buddy - pal - nothing I said contradicts the failsafe working
exactly as you described here and long ago when the channel 20 problems
first surfaced.  I had a brand new Attack AM radio at the time and sent
it back to Tower to exchange for a Airtronics FM Dual Conversion because
of your field experience.

As an aside - I received mail from Dan Snow off line about my previous
reply before I could write this one.  He said...

>From:	THOTH::SNOW         "Ballistic Panic Pilot"
>To:	KAY,SNOW        
>CC:	
>Subj:	Vision Radio
>
>Kay,
>	The November issue of Flying Models has a product review of the Vision
>8P (The power plane version). You're partially correct on the No Failsafe 
>issue.The Vision has a hold last, but no pre-set.
>
>Dan

And I replied that the Vision transmitter has no failsafe.  The Airtronics
2985 8 channel FM/PCM receiver has failsafe (the same receiver as used on
the Quantum) and therefore it will take the power up default failsafe of
"hold last".  The Experts told me (ATRICS folks) that they did not do
failsafe in the Vision because they did not believe in it for sailplanes.

Before Al Ryder flames me...
Al believes that Airtronics left it out because of technical difficulties.

Bye
Kay R. Fisher (who now owns a Vision but doesn't have possession).

    I've only been silent because I've been absent.  I'm throwing in my 2
    cents for PCM.  The thing that makes it so much better than other
    available methods is the 'glitch free' operation.  Kay talked about a
    possible interference affecting the pulsewidth of one channel on an FM
    set but really what usually happens is that an extra pulse (possibly
    from an interfering tx) gets in and causes the decoder chip to lose
    sync.  Now what happens is the pulses get sent to the WRONG channels
    and the unused ones that usually are full on or off cause you to get
    full up elevator or down, full aileron deflection, etc.  Ask anyone who
    has been shot down what that's like.  If the interference is not too
    severe, the receiver doesn't lose sync too often and the servos don't
    move that far because most of the frames are right.  If you have a
    direct interfering source, neither system will get valid data but the
    PCM system will fail in a more controlled manner.
    	Kay is right that PCM costs more, but one of my planes has a $300
    engine up front.  You can get a dual conversion PCM set for just over
    $200 if you don't want lots of bells and whistles.  I think it's worth
    it to me.  My Airtronics Spectra PCM sets have not missed a beat in a
    season of flying.  My old AM set got shot down at CRRC by a TX being
    left on with the antenna down.  I am sure that my PCM would not have
    even noticed.
    
    Charlie (a happy PCM owner)

Re: .169  Charlie Watt

[...]You can get a dual conversion PCM set for just over
    $200 if you don't want lots of bells and whistles.  I think it's worth
    it to me.  My Airtronics Spectra PCM sets have not missed a beat in a
    season of flying.

Ok Charlie, you got my attention. Whose and where. I'd also consider a cheap
set this year (to get dual conversion and PCM) if it provided a migration path 
for more features next year. For $500 I need to get EVERY feature I'll need in
the near future. For $200+ I can afford to start off with something which gives
me servos and a "back up" Tx once I do get the high end set (they might even 
come down in price by the time I need those "other" features) I'm basically a 
sport flyer with interest in a Panic and a V tail glider half built due to a
hatred of the included mechanical mixer. Tell me more (was this $200+ radio the
one you had in the Panic at the fun fly?)

    Just another word for Futaba.  If you'll take a look at the matrix of
    Nat's pattern winners in the Current issue of Model Aviation, you'll
    note that the top-6 finishers in FAI pattern flew Futabas and no less
    than 14 of the top 20 also flew Futabas.  Also of interest was that all
    5 of the finishers listed in Expert flew Futaba.  As a matter of fact,
    Futaba clearly dominated the radio preference in ALL pattern classes
    with JR running a very distant second.  I don't stay close enough to
    pattern to know if there's any significance to it but not one solitary
    Airtronics was listed.
    
    Slightly off-subject, I noted that YS was the clear preference for
    engines with O.S. running a distant second.
    
    Anyhoo, if the choice of the pros cuts any ice, it would appear that
    Futaba is THE choice for radios, going away...seems like a pretty fair
    recommendation to this here cowpoke.  (I just wish we could convinve
    _all_ the mfgrs that, if they can build special pattern, sailplane and
    helicopter radios, they could certainly build a SCALE radio!)

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

>Ok Charlie, you got my attention. Whose and where. I'd also consider a cheap
>set this year (to get dual conversion and PCM) if it provided a migration path 
>for more features next year. For $500 I need to get EVERY feature I'll need in
>the near future. For $200+ I can afford to start off with something which gives

Well - I'm not Charley but Charley flys Airtronics and the $200 PCM is
the Vanguard 4 ch FM/PCM see sheldons latest add in RCM for exact price
(I had it here at work yesterday - but not today).  But you don't want
the 4 channel - for another $38 (approx) you get the 6 channel.

Now - I'm not sure if it has the vtail mix on it (Charley does it).

But the main reason I'm jumping in (again) is because you talked about
this as being an migration path.

Don't assume that.  The Vanguard PCM receivers are NOT compatible
with the Vision and Quantum receivers.

If you look at Futaba and JR I believe you will find the same
compatibility problems.  Al Ryder did quite a bit of research on this
and his finds are hidden in this file some place.

So before everybody flames me for putting out bad data on Futaba or
JR - please wait for Al Ryder to clear up the PCM migration compatibility
question.

So before you get a Vanguard 6 ch FM/PCM:

	1.  Make sure it has V-Tail coupling
	2.  Understand that you can never talk to it with a Vision or Quantum Tx

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    I'm pretty sure that all JR systems offered today can be run from
    their top of the line radio, the PCM10.  I run my Century VII RX's
    from the PCM10 on PPM.
    
    As Eric stated, for programability you have to pay. 
    
    
    Tom

>< Note 105.167 by PNO::CASEYA "THE DESERT RAT (I-RC-AV8)" >
...
>    understanding/setting up a 1024.  The other thing is that ALL PCM's (to
>    my understanding) use the 5-bit microprocessor developed by Futaba when
>    it introduced PCM a few years back.  ALL, that is, EXCEPT for Futaba
>    themselves who have upgraded to a 10-bit microprocessor  (hence the
>    "10"24).  Eric has commented that PCM's are not quite as smooth to the
>    "feel" as conventionally modulated systems due to the 5-bit
>    microprocessor.  This is precisely the reason Futaba went to the
>    [exclusive for the time being] 10-bit; it's the next natural step in
>    the progression of the state-of-the-art.

Hi - it's me again - just trying to create more confusion.
I read the same article (but I forgot where) and they made a typo.
Every reference to the 5 should have been an 8.  What the guy meant
to say was the size of the word used to store the analogue values
was stored as a smaller size prior to the Futaba 1024.  The 1024 has
a 10 bit representation of the stick positions - this represents
2^10 possible locations = 1024 possible positions of the servo.
Prior (and perhaps all other vendors) PCM systems used less bits to
represent a stick position.  But it wasn't 5 - 2^5 is only 32 possible
positions and that would be unusable by anybody.  But he meant to say 8.
which means that previous Futaba PCM systems had 2^8 = 256 possible servo 
positions and most micro processors are 8 bit machines also.  Airtronics 
claims that they choose to have faster repetition rates rather than high 
resolution.  Apparently the jump is so small that even Futaba made special 
servos to go with the 1024 systems.  The servo itself is still analog and 
has knowledge of bits per word.

High accuracy servo positioning is probably part of expert pattern and
it would not surprise me if the reason so many in pattern choose Futaba
that it is because of the 1024 feature.  The same reasoning applies
to why Eric can feel the difference - he is an expert flyer.

The Airtronics Vision uses 8 bit bytes for stick positions.
If you go into the stick function test you can vary the digital
read out from 0 to 255 and sticks center around 128.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

The World Engines Expert and Polk's Aristo are two strong 1991 FM
radios, but I question the price: its just too cheap for my
comfort.

Their 4 channel PCM is a very nice radio for under $200, and it
does have some added functions -- this is a real last-ditch
contender for cheap bullet proof entry into 1991.  The Futaba and
Airtronics radios for less than $100 more are a big jump up in
sophistication and quality (did I just say something nice about
Futaba?).

Again, I ask this question in this topic: has anyone, or can
anyone, check the Expert/Aristo FM receivers for compatibility
with Airtronics Vanguard FM/Vanguard PCM in the FM mode?  This
would be a very gigantic plus for the Airtronics, giving access
to cheap flight packs for second-line planes.  

    Eric,
    
    In all fairness and honesty, I'd be happy to post the TOC stats and who
    bought their own radios except for the fact that I've never run across
    such info...as I mentioned, I don't stay up on pattern at all and, but
    for the current discussion in this topic, I'd have paid little (if any)
    attention to the pattern results matrix in the current Model Aviation.
    If you posess this info, by all means make it public.
    
    As [I believe] we've both said, I think it'd be difficult to get a bad
    [PCM] radio, no matter who's name is on it nowadays...it's all in
    personal preference; you like JR, I prefer Futaba and I think we both
    win.    

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

>< Note 105.158 by MDSUPT::EATON "Dan Eaton" >
...
>Also from the same RCM on page 132 is an add for Sheldon's Hobbies new
>'bullet proof' replacement reciever. It looks impressive and the 
>introductory price of $60 sure can't be beat. (Usual diclaimers) Any
>comments?

I checked out the add.  Looks pretty good and is a good alternative
for Futaba FM future purchasers.  Since I ordered 2 FM Airtronics
receivers from Sheldon's yesterday I had to consider this alternative.

It is a 7 channel Dual Conversion for $60.
It comes in AM or FM with Airtronics or Futaba connectors (4 receivers).

Price does not include any servos, switch harnesses or batteries.

The Airtronics 6 channel FM Dual Conversion is $64.

For $4.00 more I have a radio I can send back to Airtronics if I
have any problems and I trust them to still be in business in a few 
years.

Also even tho they claim AMA Certification - they like Futaba are
not in the latest list published by the AMA every month in Model Aviation.

They claim to be the FIRST AMA Certified receiver.  That's a typo - 
what they meant to say is the FIRST AMA Certified AM receiver.

Again - the AMA does not certify anybody - they just publish lists
of independently certified radios.  So when this outfit makes it to
the AMA list and assuming they beat Futaba there then indeed their
radio may be the FIRST AM certified.

Is it a good buy - probably but like Futaba they will have to make
it to the AMA list before they will get my money.

============================================================

A lot of you think I've been bad mouthing JR and Futaba lately.
Not at all - If money was no object I would probably want a
JR PCM 10 - not that I need 10 channels but I like the radio.
The cost consideration is not so much the price of their one
transmitter but the cost of additional receivers and servos and
spare parts.  I own one JR century 7 single stick and cringe
when I need a part - in fact Eric rescued me from their sales
ignorance.

If money is an object - but time wasn't then I would pay $669
for the Futaba 1024 PCM9.  I just want to wait for them to make
it to the AMA list.

Now all money and time considerations aside - IMHO Airtronics
makes the best sailplane radios.  So although I might prefer another
vendors radio for powered planes - sailplanes get my Vision.
The Vision is not perfect by any means.  It needs:

	1. A clock
	2. 1024 bit resolution
	3. Better ergonomic engineering (round sides and grippy back).
	   Even the Futaba Attack has better grips.
	4. More memory (it can only store 4 planes (I already have 4 receivers
	   for it and 4 sailplanes (actually 1 done - 2 in progress and 1 for
	   Xmas)), also you have to represent plane selections with numbers
	   instead of ASCII names.
	5. You cannot program the flap stick like a throttle.  (The flap
	   stick is what most of you think of as the throttle in the first place).
	   This stops it from being a good general purpose transmitter for both
	   sailplanes and sport power planes.
	6. It only comes with a PCM receiver.
	7. Airtronics does not make a 1991 Dual Conversion micro receiver - YET.
	8. It only comes with servos.  There are lots of types of servos
	   and it would be nice to package them separately.
	9. It only comes in black.  I would prefer emerald green with leather.

Am I rambling yet.

For all it's faults - It is still the best sailplane radio made.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

Re: .172

I stated in my reply that I'd consider a $200 radio as part of a migration path
not an end unto itself. The migration would mean that I could use it for second
line airplanes and swap Rx & Tx to upgrade (I wouldn't loose my servo investment)
I guess I'm not as savy about the servo technology nowadays. I used to have to 
buy the manufacturers servos to be used since some of the intelligence was in it.
I see that this isn't the case these days (I'm glad). I also stated that I was
looking for something that had some number of features (most bang for the buck).
I've got no problem with a $350 JR radio if it gets the job done but as the 
price tag grows I want more features. My price ceiling is around $500 but it 
better be a damn good radio that I'll be happy with for a lot of years. I've got
a lot of justifying to do as the price goes up. I meant that I would consider a
straight 6 ch FM (PCM?) dual conversion radio in the $200-300 range IF I could
use pieces of it with a later purchase with all the bells and whistles.

The mixing will be more important as time goes on (next year) and could be 
addressed then. I'm flying a Futaba Attack AM to get back into the hobby and I'm
looking at how I can upgrade my gear as these needs come about.

I'm looking at FM to help with the constructive/destructive interference issues.
I'm looking at dual conversion for the 3IM issues with 460 interference in the
455 intermediate stage. I'm looking at PCM because I have written disk CRC code 
and feel comfortable with the theory that is behind it (how about single bit 
correction and double bit detection? 44 bits gives you 36 you can believe in.)
I just have a far better capability to justify incremental purchases rather than
going out and dropping >$500 on a "toy" than rebuilding a $100 plane and clean 
out a $100 engine. I've crashed a lot but haven't bent an engine seriously 
(other than needle valve type stuff) since my parking lot C/L days. I'm back in
the hobby mostly due to having hauled my stuff from house to house and 
accumulating things over the past 20 years. I've got >$1000 in pre-1991 Heathkit
and Kraft radios that I don't want to have thrown in my face when I ask about
buying the latest and greatest radio widget.

Oh well, back to real work

>    Food for bit-heads here is, "How often does the second style of PCM,
>    eg. auto-load, send the failsafe settings settings to the RX memory?".

Exactly the kind of question that I like.

Now we're getting down to earth.

Given that we don't have a copy of the microcode.

Here is how I would do it.

One bit in the ID byte would mean that the other bytes are the new failsafe
settings.

Keep a 1 byte counter.
increment the counter every time I transmit a packet that is not
a "load new failsafe" packet.

IF the counter gets to zero 
AND if the stick positions are equal to the last transmitted stick positions
THEN
	send a "load new failsafe" packet.
ENDIF

This way the user should never see the transaction and the Receiver will
get the new info often enough to insure he is up to date.

=================================================================
Can you see some poor guy who doesn't understand the new computer
radio terminology.  Here he is flying 4 mistakes high and suddenly
he starts getting hit.  His plane goes into failsafe and flys
in nice gentle circles - but he realizes he has no control.

What does he do?

Obvious - he reaches down and presses the "FAILSAFE" button!

ARGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

re Note 105.174 
    
>>  .......................  Al Ryder did quite a bit of research on this
>>  and his finds are hidden in this file some place. ......... please 
>>  wait for Al Ryder to clear up the PCM migration compatibility question.

    I only found some of the answers and documented only some of those,
    but FWIW see Note 1047.7 and some of the later entries.  Also on
    this general radio selection topic, see the entries pointed to in
    11.114, 11.115, ....  ( keyword=RADIO* )
    
------------------------------------------------------------------------
    
    The dialog has strayed from 1991 considerations to the more generic
    topic of modulation schemes and the various manufacturers.  Sometime
    over the weekend I'll move much of this to note 51, the discussion
    on radio selection.  Please continue this healthy dialog here until
    the move and there after.  Thank you.

Hi,

This may belong with note 51, but here goes......
    
I think some confusion of terms may be happening here.

AM and FM are modulation methods. The modulation is used to carry the
encoded information.

PCM and PWM (or PPM) are encoding techniques although the M in the
acronym stands for modulation - confusing eh.

Dual conversion is a techniques to improve the
radio frequency rejection of our (super-hetrodyne) receivers.

A dual conversion set may use AM or FM modulation, and/or be encoded in
PCM or PPM, they are as such non-related. There are some technically
inferior combinations of the above that will probably never get implemented.

Specialized transmitters can be implemented for all of the above, however,
    implemention/user interface is made easier using digital processors,
    but they can and do ouput a signal in AM/FM, PPM/PCM.

Let me explain briefly or not so briefly:

AM - amplitude modulation
-------------------------

 Strength (or amplitude) of the "carrier wave (CW)" varies with the information
 being sent.

 Advantages

	This is a simple modulation technique to modulate in the transmitter
	and demodulate in the receiver.
        Early designs used this because with the current state of electronics
	anything else would have been too bulky and/or costly.

 Disadvantages

	Turning the carrier on and off causes a large area of the rf spectrum
        to be taken up by whats known as sidebands of the carrier. These also
        appear at other muliples of the carrier frequency (harmonics).
        So bottom line is - difficult to get a clean signal that doesn't
        either use too much of the crowded airwaves, or interfere with other
        non-related users.

        The AM demodulator in the receiver gets overloaded by high signal
        strengths, so some form of automatic gain control (AGC) is needed.
        Its difficult to make the receiver selective (i.e. have a narrow
        response) to the desired frequency.
        A result of this, is if you fly near someones TX thats on a close
        frequency, enough of the signal can get in, this causes the agc to
        act and lower the gain, perhaps lowering the gain enough so your
        lower signal strength transmitter can't be "heard".

        Impulse interfence consists of a wide rf spectrum of changes in
        signal strength i.e. it looks like AM.
        So AM receivers have poor impulse interfence rejection.

FM - frequency modulation
-------------------------

 Frequency of the signal is varied (deviated) from the center frequency
 according to the information being sent. The signal strength itself is
 constant.

 Advantages

        Can be made to produce a narrow band clean signal.
        Does not need an agc circuit so not so badly affected by
        proximity to stronger transmissions.
        Impulse interference rejection is greatly increased.


 Disadvantages

        Closer tolerence components needed (e.g crystals).
        More complex circuitry needed.


PWM/PPM - Pulse Width (Modulation)

 Each control function (channel/stick) is represented by a pulse. The width of
 the pulse (in time) is proportional to the stick position. Many different
 widths have been used in the past, but the "standard" today is 1 to 2 millesecs
 (1000ths of a sec), center width 1.5mSecs.

 All these control pulses are arranged in a pulse train (frame), with inter
 pulse gaps.The last pulse in the frame is known as the synchronization pulse,
 it always (now adays) much wider than the channel pulses. many different
 frame repetition rates have been used, but the "standard" is 20mSecs. So as
 the control pulses have defined limits, the sych pulse is varied in width
 to make up the overall frame size in time.

 e.g. channel 1,2,3,.....,synch,1,2,....

 Often called digital proportional, but its really analogue.
 

 Advantages

 In the early days of electronics, this could easily be implemented using
 transistors in the encoder, decoder and servo amplifiers.
 As a progression, low current computer integrated circuits were used
 to reduce the cost, these have been replaced in recent years by specialized
 integrated circuits.


 Disadvantages

 Interference manifests itself by either obliterating the proper channel
 signal. This leads to the servo receiving an interference generated pulse
 width. If the interference pulse is long enough, it gets confused with the
 synch pulse, causing a loss of frame synchronization. This results in
 the servos receiving either noises pulses, or some other channels valid
 pulse.

 So net effect is the servos see a wrong command and act on it i.e. glitch

PCM - Pulse Code (Modulation)

 This is using computer techniques. The transmission follows a data format
 protocol. Stick positions are represented by a sequence of numbers. Checks
 can be made to see if valid data is received.

 There are several different types, so no two manufactures equipment
 typically works together, unlike the AM (and usually FM) PPM sets.

 Most manufacturers have even modified the encoding since the early days
 of PCM.
    
    It should be noted that the PPM servos are treated as a standard, so
    PCM receivers output a PPM signal to the servo, of 1 to 2 mSecs pulse
    width. So your flight pack (except those connectors) can be re-used
    assuming they have been checked out as a1.

 Advantages

 Provides best interference rejection today. With future enhancements
 we may be even see error correction like on todays computer systems.

 Most sets can be programmed remotely for signal failsafe and some
 allow a rx battery failsafe to be set.

 Disadvantages

 Cost is high at present, but as with all electronics, likely to fall
 relatively.

 Marginally higher current drain, and slightly bigger receiver size.

 Once you've gone for one manufacturer you are stuck with it for extra
 flight packs.



Overall

 You can witness the difference between AM/FM PPM/PCM systems in your
 own home.

 Your Hi-fi has undergone the same revolution as we are experiencing.
 Transmission used to be AM, but the quality was poor so they moved to
 FM (other reasons here too).
                                               
 We used to have records, but these have been ousted by the cd.
 No more hiss, crackles and pops to spoil your enjoyment, even error
 correction !!!


    

RE:  Note 51.60 by MOVIES::COTTON - Mark Cotton

Mark,

First of all, thanks for a very clear description.  Personally, I've
understood these terms in the past, but I'm sure many of the notesfile
readers now have a better understanding of these terms thanks to your
note.

>> This may belong with note 51, but here goes......

Looks like the moderators moved it for ya'...
    
>> PCM - Pulse Code (Modulation)
>>
>> This is using computer techniques. The transmission follows a data format
>> protocol. Stick positions are represented by a sequence of numbers. Checks
>> can be made to see if valid data is received.
>>
>> There are several different types, so no two manufactures equipment
>> typically works together, unlike the AM (and usually FM) PPM sets.
>>
>> Most manufacturers have even modified the encoding since the early days
>> of PCM.

Do you (or anyone in the notesfile) know the *EXACT* details of any (or
all) of these data formats?  For example: 

"For radio manufacturer XYZ, the format is:
  Each bit is transmitted using Manchester Phase Encoding.  
  Each frame contains:
    - 6 bits of sync (all zeros)
    - 7 groups of 10 bits each for channels 1 through 7 
        (for each channel, the most signigicant bit is transmitted first)
    - 16 bits of CRC computed with polynomial X^16+X^15+X^1+X+1 "

Essentially, I want enough detail that I could actually build a
transmitter that would talk to one of company XYZ's receivers.  
(Or visa versa - I could build an Rx to listen to one of their Tx's.)

                       _____
                      |     \
                      |      \                          Silent POWER!
      _        ___________    _________   |            Happy Landings!
     | \      |           |  |         |  |
     |--------|-  SANYO  + ]-|  ASTRO  |--|              - Dan Miner
     |_/      |___________|  |_________|  |
                      |       /           |     " The Earth needs more OZONE,
                      |      /                       not Caster Oil!! "    
                      |_____/

    
    
    While we're at it, has anyone opened up a PCM transmitter to see
    what microprocessor they use?  If it were reasonably easy to get
    at the firmware it might not be too hard to add features to the
    cheaper PCM systems.  Things like saving trim settings for multiple
    planes for example.  Unfortunately that doesn't do us much good if
    we can't buy reasonably priced PCM receivers.
    
    I'm wondering if they use a micro with a serial port to generate
    the "pulse code" serial data stream, or have dedicated hardware
    that works off bytes or words of data from the micro.
    
    Anyhow, I'm just curious at this point.  I know there are some
    single-chip micros out there with built-in A/D functions, maybe they
    use one of those?  If anyone opens up their PCM xmitter, please
    list the markings on the chips in here so we can look them up!
    
    Bill

    Both my futaba PCM's appear to use a Futaba built micro. None of
    the 8XXX or 6XXX class micros. In fact I believe that Futaba states
    that they designed their own micro. One thing that I have not been
    able to assertain is if the 7,9 channel Futaba 1024 micro, is the
    same as the 5 channel 1024 that I have. If it were, I could simply
    add a few switches, and gain more channels, etc. As it is my 5 channel
    PCM 1024 comes with the top of the line 9 channel RX. 
    
    Anybody want to pull the cover off their 7 channel 1024, and tell
    me the numbers?
    
    
    						Dave
    

>From: [email protected] (Rob Logan)
>Subject: helis in chicago (long)
>Date: 8 Nov 89 21:38:30 GMT
>Sender: [email protected] (Rob Logan)
... 

>oh...  airtronics is comming out with a new
>radio..  It's going to be in a fancy black box with finger holds and a
>large touch screen.  The thing that impressed me was that you can type
>in what channel you want and the receiver will match it! You will never
>be left without a freq pin!!
...

I had insider info that this was coming.  Now what someone else has
talked about it in public this brings up several issues worth discussing
in general.

How do you feel about someone having the ability to change to your channel
at will?

I would hope that they do something extra so that you can't just change
channel numbers so easily.  For instance require that you stick a key
in the side.  One that you could put a tag on and leave at the transmitter
impound.

Can you see when your receiver gets low and the micro processor goes
berserk.  It starts incrementing the channel number.  Headlines read
"Dave Walter empty's sky at annual CRRC meet."
Dave refused to be interviewed but it is said he had one of the new
Futaba computer radios and even tho they are not AMA approved yet he
bought one anyway.

Are you awake Dave.

Anyway I am glad they finally produced a box with ergonomic engineering.
I'm just a bit curious how they implemented the Receiver switching.
My guess is they have an umbilical cord to the Transmitter for changing
frequencies just like JR can plug their Transmitters into the Receiver
to adjust Servos without Transmitting RF energy.

Maybe if I could get a receiver that sniffed frequencies it could find
a better pilot in the middle of a flight :-)

So what do you think about synthesizing frequencies?  

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

Huh? What? How did I get dragged into this? I was just minding my own business,
and the next thing I know I'm shooting down everyone in the the sky.

The frequency synthesis just sounds like an easier way to change channel than
pulling out a crystal and putting in a new one. I'll bet the receiver still
runs on one channel ONLY.

As for changing channels as the battery gets low, I think you can design a 
lockout circuit that prevents that from happening at low voltage. I suspect
that's needed anyway to save setups for different planes. Do they use an
Electrically Eraseable PROM for setups?

Dave

    
    I don't see much value in a synthesized system that doesn't allow you
    to change the receiver frequency too.  It's bound to cost a lot of money,
    so you'd better get more than that!
    
    I think if done properly they will be the wave of the future, even
    though some systems were out quite some time ago that had this feature
    (selected on Xmitter and Rcvr via switches) and never caught on.
    
    I wouldn't be nervous about them when flying with the 3IM crew at
    lunchtime,  in fact they'd be very handy to avoid frequency conflicts.
    But I'm real scared about people who have trouble setting the time on a
    VCR getting their hands on one!  Let's hope they put a lock and key on the
    feature and display the channel number clearly on the display.
    
    Bill

    Kraft used to have this feature and it was more commonly refered to as
    "Dial a CRASH".
    
    I put a entry about this where it was posted in the chopper notes:  
    
    Kay I wonder who your inside info was from.....
    
    I have been in contact with Tom and Gene of Control Systems Labs and I
    am pretty sure that they are responsible for this, they are the ones
    who brought airtronics the ATRCS that went on to be the VISION.  Ok
    guys better start dumping the Futaba stuff now and get ready to jump on
    the band wagon.
    

    in the hands of a bozo, programmable frequencies could be deadly.
    theres the danger that someone would reprogram their xmitter and
    forget what freq it was set to that day.
    theres also the danger that someone would reprogram to avoid all
    other xmitters when they show up at the field, then become
    lackadaisical about freq control even as new fliers (xmitters)
    show up at the field later.
    
    however i think being able to avoid other xmitters on the same
    freq is too valuable.  i've seen even good friends who fly with
    each other regularly shoot each other down!  from what i've seen,
    the most common cause is someone forgetting to turn off, the other
    being forgetting to check before turning on, either forgetting pin
    or taking wrong pin.  the benefit (to me) outweighs the danger.
    
    i still like the idea of standardizing pins and xmitters so that
    you can't turn on unless the pin (key) is inserted in xmitter.
    
    k
    

I went to a club meeting last night at Ray's in Worcester and he mentioned that 
Futaba is coming out with a new line of FM and PCM gear after the first of the 
year that is all dual conversion and feature rich. Anyone else heard similar or
additional rumors/facts. Sure would be nice if I could continue to use my 
J-connector servos and get the new features I'm looking for...

    Pikes Peak Soaring Society has adopted a policy to help prevent
    shootdowns and I believe we have only had 1 this year compared to 3-4
    last year.  What we try to advocate is that unless you have the pin and
    flying, in addition to checking that your off is to collapse your
    antenna, if you antenna is collapse even though your radio is on you
    lessen the chance that you will shoot someone down.  I have even tried
    this on accident and yes there was someone flying on my freq when I
    went back to my plane to check something and noticed my controls were
    wiggeling.      GOOD thing my antenna was collapsed.  Somewhere I seen
    that you would have to fly about 2-3 feet from the collapsed but still
    on TX to cause any effect.   Well it helps anyway, Those little
    switches are tough to remember, also I can take a gaze at the other
    people on my freq and see if their antenna's are down.

RE:

>							Somewhere I seen
>    that you would have to fly about 2-3 feet from the collapsed but still
>    on TX to cause any effect.   


   WRONG!  I know from experience that this is not true.  At least with AM
radios that is.  At the last CMRCM fun fly this year I was very nearly shot
down by a radio in the impound that was left on with the ant. collapsed.  
When the radio was between me and my plane I experienced severe interference.
It was only my awesome piloting skills that allowed me to save my plane.  I
know.....I know.....get back to reality..... 8^)



			Jim

    
      I also was nearly shot down a coupple of weekends ago by a
    Transmitter that was left on in the Transmitter impound. The antenna
    was also collapsed. Granted, by being collapsed, it did increase my
    chance of landing intact (which I was barely able to do), but it is
    by no means absolute insurance of not getting hit when flying with AM
    radio's.
    
                                                 Dan
    

    Re: .70, Jim,
    
    The current new generation of Futaba 1024 PCM's is _already_ compatible
    with your "J" series and "G" series FM connectors.  I know this to be
    fact as I have one each of the above sysetems and all servos, plugs,
    harnesses, etc. are interchangeable.                                 

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

    re: .my last reply....
    
    Mr. Chairman may I please withdraw my last statement....
    
    OK OK so its not a guranetee but it is some added insurance.
    
    Mark

>< Note 51.62 by LEDS::LEWIS >
...
>    use one of those?  If anyone opens up their PCM xmitter, please
>    list the markings on the chips in here so we can look them up!
    
Bill, the Airtronics Vision has a large square chip in a carrier
with 17 pins on each of 4 sides.  It has two numbers on it.

S8818

and

HPC46003V17

Also close on the board is a 16 MHz Xtal and a couple of ROMS.
Three or 4 jelly bean xx74xx parts.  Not a lot of real estate.

So what is a 8818 - some special purpose relative of an 8088
with I/O functionality on board?

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

>>Bill, the Airtronics Vision has a large square chip in a carrier
>>with 17 pins on each of 4 sides.  It has two numbers on it.
>> S8818  and  HPC46003V17

    I'll bet that the "8818" portion is the date code of when the chip
    was manufactured: the 18th week of 1988.  I think the part # is
    "HPC46003V17".  What part is this?  I have no idea...

                       _____
                      |     \
                      |      \                          Silent POWER!
      _        ___________    _________   |            Happy Landings!
     | \      |           |  |         |  |
     |--------|-  SANYO  + ]-|  ASTRO  |--|              - Dan Miner
     |_/      |___________|  |_________|  |
                      |       /           |     " The Earth needs more OZONE,
                      |      /                       not Caster Oil!! "    
                      |_____/

Anybody have an IC Master?  Mine is 1981, much too old.  I'll bet
its a custom logic array.

    
    I agree the 8818 is probably the date code.  If it's the controller
    and also the chip that does the A/D conversions for PCM it couldn't
    be _just_ a logic array.  Maybe it's one of those one-chip
    microprocessors that have an analog channel.  Unless there is an
    external A/D chip that Kay didn't notice.  Of course it might be a
    custom in-house design, in which case we're out of luck.  I'll look
    around for that part number though.  Thanks Kay.
    
    Bill

    
    Ok, I found it.  Well, close enough anyhow.  My National Semiconductor
    book has an HPC46004 which is probably the same chip with very slight
    differences from the -3V17.
    
    It's a single-chip micro-controller with -
    
    		16-bit architecture
    		8-channel 8-bit A/D converter (6.6us conversion time)
    		Four 16-bit timers/counters
    		16x16 multiply and 32x16 divide
    		16KB on-board ROM
    		512 bytes on-board RAM
    	        interrupt controller
    		UART
    		... plus a bunch of other nice features.
    
    I'm glad they used an off-the shelf part.  This leaves many hacking
    possibilities!!!  Now I have to scrounge up the $$$ to get one.
    Maybe if I drop enough X-mas hints...
    
    Bill
    
    p.s. has anyone else opened up their PCM systems???

Them's thats gonna get the Vanguard PCM had better get gettin
now.  Just got the new Tower catalog -- from $238 to (gasp) $309
for the PCM 6, and from $one-something to $224 for the FM!
Really screws up my arithmetic, I thought new models would force
the price DOWN.

I hope this is a Tower-only thing, done to push their Futaba and
Kyosho lines.  But in the least it will remove Tower's pressure
from the other distributors and they'll probably raise the price
too.  The next issue of RCM will tell the tale if its an
Airtronics increase.

That new Kyosho radio is mighty fine looking, but I have my heart
set on an Airtronics.  Looks like it'll be the FM for me. 

>      <<< Note 51.81 by CTD024::TAVARES "John -- Stay low, keep moving" >>>
>                        -< Get 'em while they're hot! >-
>
>Them's thats gonna get the Vanguard PCM had better get gettin
>now.  Just got the new Tower catalog -- from $238 to (gasp) $309

$239.96 (6 channel) in Sheldon's

>for the PCM 6, and from $one-something to $224 for the FM!

$159.96 (6 channel) in Sheldon's

>Really screws up my arithmetic, I thought new models would force
>the price DOWN.

I bet you've been looking at their new "LARGE" catalogue.
Don't panic.  Prices in the large book are always XXX percent over
what they offer in the Tower Talk flyers and they have always been
offering the Airtronics line as at least line items in the flyers.

>I hope this is a Tower-only thing, done to push their Futaba and
>Kyosho lines.  But in the least it will remove Tower's pressure

I've been compiling an order over the last week and have consistently
found lower prices for nickel dime stuff thru Sheldon's.  I'm not sure
what is going on with Tower but it would seem that we are finally paying
for their marketing crap (sweepstakes, phone specials, etc.).


Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    
    I forget if it was mentioned before, but does the Vanguard come with
    an 8-channel receiver?
    
    Also, has anyone looked inside the receiver?  I'd be interested in
    what chips are used in there as well.
    
    Bill

Dan Snow asked me to verify this offline, so, sad to say, no
mistake.  I had planned on comparing the '89 prices too,
but there is a typo in the '89 catalog; this is the best I can
figure out with what I have:

				VG6DR (FM)	VG6P (PCM)

Airtronics '89 Price		319.95		389.95
Tower '89 Price			219.95		269.95
Airtronics '90 Price		319.95		449.95
Tower '90 Price			224.95		309.95

As Kay pointed out, the Tower big catalog price for '89 is higher
than the Tower Talk price; the VG6P got up to $248 and change in
the last issue, and you see it listed as $269 here.

Happy Holidays From Tower!

    
    I confused myself (so what else is new, they ask).  Kay was talking
    about the Vision and for some reason I was thinking Vanguard.
    So, my next question is...  do they use the same chip set in the
    Vanguard PCM as in the Vision?  Charlie thinks no, that the Vanguard
    might have some cheapo PCM encoder without a microprocessor.
    
    I was hoping that I could buy a relatively cheap system (prices
    in the Vanguard range) and customize it to my own needs.  Prices
    in the Vision range are out of the question.  My only hope may be
    to _really_ customize and add the microcontroller myself.  Ugh.
    
    Bill

    Topic 1047 has discussions about the differences in the Airtronics
    radios; for example, the PCM incompatibilities are described in
    [the very long] 1047.7
    
    However, I don't think the chips used are described anywhere here.

>    I confused myself (so what else is new, they ask).  Kay was talking
>    about the Vision and for some reason I was thinking Vanguard.
>    So, my next question is...  do they use the same chip set in the
>    Vanguard PCM as in the Vision?  Charlie thinks no, that the Vanguard
>    might have some cheapo PCM encoder without a microprocessor.

No way Bill.  The Vision CPU was developed (without Airtronics knowledge or 
help) by two hackers at CSL and they made magazine articles about it and sold
it independently as a MD7SP upgrade.

Even the PCM part of the Vanguard is not compatible with the Vision.
The Vision is PCM compatible with the quantum.  The Vanguard PCM
is compatible with the Spectra.  As for the CPU chips the Vision CPU
should be one of a kind but...

Good chance it is eithor used again or the CSL guys specified the new
chip for the new 10 channel and of course for the Vision II.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################
    

    
    Ok, it's starting to sink in now.  Thanks for the clarification.
    I'm not sure I understood your meaning when you said "the Vision
    CPU should be one of a kind" since they used an off-the-shelf
    microcontroller.  I'd bet all the high end PCM systems with any
    intelligence use the same (or a similar) chip.
    
    For 10 channels they probably used the same chip with an external
    analog multiplexor.  I'd be surprised if they could make enough
    money to justify paying for a custom version.  Then again, maybe
    there is a 10 channel off-the-shelf chip out there somewhere.
    
    I've decided that my next system will be PCM.  I am going to
    pursue the possibility of customizing my own.  I will probably
    start with a good quality 1991 FM set (so the transmit/receive
    part is good) and go from there.  If anyone is interested in such
    a project (Charlie and I have already talked about it and he seems
    interested) send me mail.  I won't clutter this topic any more
    with this stuff - if warranted I'll start a new note in the future.
    
    Bill
                 

    After getting the radio installation done on the Fiesta, I remembered
    that I hadn't checked the throws for any of the control surfaces,
    espically the throttle. So, I hooked up the battery, put the wing
    on and began to check everything out. The throttle WAS way off and
    in the process of adjusting everything, something strange happened.
    
    After about 5 minutes of adjusting, each time I called for full
    throttle, the servo would go full swing, then bounce back and forth
    between half throttle and full throttle. It did this for about 2
    second, and then would stop at the full throttle setting I was asking
    for. Going back to low throttle was normal. It did this each time
    I went to full throttle. As time went on, it got worse and worse
    in that calling for full throttle, I would only get half throttle
    and the servo would go crazy for a couple of seconds. It eventually
    got to the point where the servo wouldn't move at all, just jitter
    a little. All the while, and even when the throttle servo wouldn't
    respond anymore, the other control surfaces were working normally.
    
    At this point I figured one of two things was wrong. Either there
    was a loose/semi-broken wire in the servo that eventually went
    completely bad, or the receiver hadn't survived the crash as well
    as I thought and the throttle input was messed up.
    
    I took the receiver pack out and put it on the meter. It read about
    4.8 volts, which, for all practical purposes, is dead. But, everything
    was still working. I charged it up over night and put it back in.
    Low and behold, the throttle was back to normal. I played with it
    for about 10 minutes and it stayed normal.
    
    At this point, I wanted to get a discharge curve on the receiver
    pack anyway, so I charged it back up for awhile, and charted the
    curve. I stopped when the pack was back down to 4.8 volts. Put it
    back in the plane, and the throttle was gone again. All other control
    surfaces worked normally.
    
    Now, I'm aware that on some of the more expensive Airtronics radio's,
    like the VG6 PCM, there is a low receiver battery warning built
    into the circuit. The warning causes the throttle servo to cycly
    up and down letting you know your battery is about dead. Where I
    was able to duplicate this, it looks like I have basically the same
    thing in the Vangard VG4R, however it's not documented anywhere
    in the manuals. So, I'm not sure if this is a "feature" or a problem.
    
    Has anyone run into this with the Vanguard series radio's or know
    if this feature is, in fact, built in???????
    
    Steve

>                       <<< Note 105.159 by RVAX::SMITH >>>
>                     -< Interesting feature or problem??? >-
...
>    I went to full throttle. As time went on, it got worse and worse
>    in that calling for full throttle, I would only get half throttle
>    and the servo would go crazy for a couple of seconds. It eventually
...    
>    I took the receiver pack out and put it on the meter. It read about
>    4.8 volts, which, for all practical purposes, is dead. But, everything
...
>    Has anyone run into this with the Vanguard series radio's or know
>    if this feature is, in fact, built in???????

Steve - this may be un-related but in my Sagitta which has the Vanguard
4 channel receiver the spoilers have been driving me nuts.  Sometimes
fully open they wander around - sometimes not.  Usually if I just
fiddle with them a bit them stop acting up - but not always.  It is an
old servo (don't recall of hand if it is Airtronics or Futaba cause I'm
always cutting wires off and re-soldering servo leads) and up till now
I have always assumed the servo pot was dirty and planned to take
the servo apart next time it comes out of the plane (after a good crash).

But hearing your story got me to thinking...  Also I am not sure it is
in the throttle channel or not?  It definitely was when I was using
the Vanguard Transmitter but when I switched to the Vision I had to move
a couple servo plug channel assignments.

Also I wouldn't consider 4.8 Volts low.  

I think they both sound like bad servos to me.  Like you was glad it
was that channel that was flaky.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

I think the first thing you should do is determine if it's the receiver or the
servo. So just swap servo channels at the receiver. If the problem stays with
the servo, the servo is bad. Otherwise, it's the receiver. I would definitely
open the servo and check it out. I wrote a little piece in here a month or
so ago about a servo that failed on me in flight. One of the wires to the pot
broke off. It was easy to diagnose and fix.

Dave

    My Futaba 1024 PCM has a feature such as this. When RX bat is getting
    low the Throttle servo will go from open to idle. It can be reset by
    moving the stick to low throttle back up to desired position. This
    is a gentle reminder that the RX bat is about had it... All others
    controls work fine. When I first got my radio, it too had a low RX bat
    and I found out how it worked. Mine however is documented.
    
    
    
    						Dave
    

You should not consider a receiver battery low until it reads
4.4V.  Your 4.8V reading is nominal.  The battery pack will read
about 5.3V for about 10 minutes after you turn it on from a fully
charged condition; then it should drop to 4.8V for about an hour,
after which you will see it drop off toward 4.4V, taking anywhere
from a half hour to an hour to do this.

I think your battery is nuked.  You mentioned that it was in a
crash.  This is usually fatal to batteries, and they must be
looked on with great suspicion until they are thoroughly cycle
tested.  If nothing else, do a load test on the battery when the
servos are hunting, if the battery reads 4.8V under load, then
you can suspect the receiver or servos; if its below 4.4V, you've
found the problem.

    Well, I just called Airtronics and here's the scoop. As far as the
    voltage is concerned, the operating range of the system is 4.8v
    and up. Any weird response below 4.8v is to be expected. They wouldn't
    even talk to me when I started talking 4.5v.
    
    Because the problem did occur at 4.8v, their first thought was a
    bad pot in either the Tx or servo. Having just returned from vacation,
    I havn't had a chance to switch servo's and see if the problem stays
    on that channel or follows the servo. I'll do that tonight. I suppose
    that would indicate a servo problem if it stayed with the servo,
    but the guy also said that it could be intermittent depending on
    voltage, or that the throttle channel from the TX could be flamming
    out at low voltage. I don't know how you'd tell if it was a TX problem
    or receiver problem, given that possibility, if the problem stayed
    with that channel.
    
    tSo, the best thing to do is send it back. Being less than a year old,
    it will get priority treatment and the turn around will be about
    2 weeks. Better safe than sorry I guess.
    
    Thanks for everyone's input.
    
    Steve

    Priority treatment, Ha I doubt it. My Futaba 1024 PCM went to out at
    less than 90 days.. Too bad for me, had to wait in the 7 week queue
    just like everybody else.
    
    
    			Best of luck...........Dave
    

    What you don't know is that in your case, when we found out you
    were sending it back, we called Futaba and told them to take their
    time so we could  have 7 weeks of peaceful flying. 8^)
    
    Steve

    Another good weekend weather-wise. 57 degrees, calm and clear.
    The field was busy, by our standards, 6 or 8 planes flying, launching,
    or recovering most of the time.
    
    I had my Super Rieti out for it's maiden flights under my ownership,
    it's 2 years old. Have a 4 chan. Futaba Conquest AM installed, with
    uncoupled ailerons and rudder. Not a good combination as I was to
    learn. Turns are sloppy with excessive altitude lost as ailerons
    are very sensetive. So a new radio with electronic mixing is in
    order, for even more urgent reasons than flight efficiency.
    
    On the second or third of my five flights, I was on the approach
    leg just getting ready to turn onto base leg, when I got a momentary
    down elevator glitch. To brief to bother me and the landing was
    uneventful. Another flyer was taking intermittent hits on his chan.52
    Futaba AM, same freq. as mine, whenever he passed over the chain
    link fence bordering the field. This is a chronic complaint of his
    so I didn't pay particular attention to it.
    
    I put in several more uneventful and brief flights, then while
    approaching at about 50ft alt. directly over the field and about
    2 seconds after passing over another pilot standing in the center,
    I got a full down elevator hit which didn't respond to recovery
    attempts in time, and it went in nose first hard enough to rip loose
    the servo tray and rip one stab half right off the pivot pins.
    
    All these glitches were very uncharacteristic for me, so we decided
    to try a few experiments. We rounded up all the Futaba AM Conquests
    and Attack radios on the field at the time; 2 chan. 52's, one 48,
    and one 56. Placing one xtmr. on the ground 30 yards away with antenna
    fully extended, we proved that any other xmtr. on a different channel
    but within 40-60 ft. of the rcvr. would override the parent xmtr.
    and cause random severe glitching.
    
    This is a common phenomenon when walking past another xmtr with
    your own rcvr on and xmtr off but I never realized how critical
    the relative distances are with both xmtrs. on. 
    
    The sum total of all this is that my days of flying AM are now over
    at least when any other radios are on the field, and I'll be getting
    an Airtronics FM-PCM rcvr. for the Reiti so that I can use my Vision
    xmtr with it.
    
    Terry
    

    re .98
    
    So last week I bought an Airtronics 6 chan. PCM. It was 4 or 5 days
    before I could take it out of the box, other than to charge batteries,
    but when I did a check out before installation, dead as a door nail!
    
    without rambling as to how I diagnosed the problem, it turned out
    to be a bum rcvr. (good xtal). So back to the dealer I went yesterday
    and he exchanged it for a like unit no questions asked as well he
    should since I pretty well keep his kids in new shoes. This was
    the first out of the box Airtronics failure he could recall having.
    I hope this incident doesn't blow their Sigma Six statistics all
    to h--ll. In the meantime the airplane languishes sans radio, but
    at least the new one works.
    
    Terry 

    Finally got my new Vibaro (viper) sailplane finished this week.
    Yesterday was nice and there is enough daylight after work to get
    in a few test hand launches, so I was at the field by 4:30.
    
    I'm using my Airtronics Vision in it, the radio has been in use
    since last summer in another plane. Got everything assembled,
    range checked good, walked out to the center of the field, raised
    the plane over my head prepratory to a running hand launch,
    wiggled the sticks and....no right aileron movement.
    Back to the side of the field, pulled the right wing off the rods
    far enough to check the plugs on the aileron servo leads, checked
    the rcvr. plug, everything looks ok. With the plane on the ground,
    stood over and wiggled the sticks. Everything works. Back out to
    the center of the field, hold the plane over my head, wiggle the
    sticks, no right aileron....what the?.... now we're talking weirdness.
    Put the plane on the ground right there,walked around it wiggling
    the sticks, everthing works. Picked it up, no right aileron. Collapsed
    the antenna about a foot, everything works! Ok, some kind of swamping
    effect. I was there to fly, not play junior Marconi, so went ahead
    and did 6 successful hand launches. Only needed 4 clicks of down
    elevator trim to bring things into line.
    
    Last night, inside, I found that the right aileron channel only,
    is swamped when the xmtr. is held within 6-8 inches fore or aft
    of the wing or under the wing, and the antenna is fully extended,
    and is more than 30-40 degrees away from being parallel to the
    fuselage, and the plane is held at shoulder height or higher, with
    the xmtr. held in the left hand. In other words, exactly the mode
    present just before launch. I've never seen such selective swamping
    action on any other plane or radio. I'm sure it's unique to this
    particular installation, and will try re-routing the rt. aileron
    servo lead within the fuselage a little, although there's no real
    diifference between it and the others now. Be interested to hear
    about other wierd Vision phenomena.
    
    Terry
    

    
    Something that I find surprising is that it is only right aileron that
    gets affected.  I thought the good PCM systems had some kind of
    checksum or error detection on each transmission of _all_ channels.
    If true, either all channels should be correct _or_ it should
    go failsafe.
    
    So, how does the aileron output get screwed up but the other
    channels not?  You might want to give Airtronics a call and see
    if they have heard of this before and if they have a technical
    explanation.  I'd love to hear it!
    
    Bill

    re 101
    
    Off the top of my head I can't recall anything in the Vision owners
    manual that covers failsafe mode. It doesn't have the push-button
    failsafe preset feature that the lower line Airtronics 6chan. sets
    do, so any designed in failsafe feature would have to be of the
    hold-last-position type.
    
    Also, this phenomenom seems to be more RF related than bit-code
    related. At least thats the impression I get watching it. But that
    doesn't explain why it's so channel selective.
    
    Tomorrow morning is our monthly club contest so I'll be going up
    the 'ol high start with an un-debugged plane. But I do have faith
    in the radio, and it's never given me the slightest problem in 7
    months of use.
    
    Terry
    

    Terry:
    Is that the plane you'll take to the SWR? I'd like to see it.  As for
    the vision, I have not had any problems, other then how to program it
    and remembering which switch does what. There are several in our club,
    no problems to my knowlege. Everyone seems pleased. I am still getting
    used to the features available and trying to learn when to use them. 
    
    Another Subject: We just received the first shipment of fuselages for
    our club project, the Icon. They are made of Kevlar, weigh 12.5 oz. and
    are very high quality. I'm impressed. This is going to be a fun
    project. I keep everyone posted on our progress.
    
    
     
    

    re .103
    Ron: 
    Yeah, I'll be taking the Vibaro to the SWR if it flies as well as
    I hope. Also be taking the Reiti as backup with the 6 chan. but
    need to install the radio and build new stabs yet.
    
    > I have not had any problems, other than how to program it and
    remembering which switch does what.<
    
    Right On !!
    
    Where did you get those Kevlar fuselages made? Sounds pretty neat.
    I've worked with kevlar tape a little bit , in balsa fuselage
    reinforcement, and it was a real pain to work with. Normal tools,
    scissors, blades, etc. won't touch it. I understand there are special
    scissors for cutting it but have never seen any.
    
    Terry
    

I instigated a discussion on the failure modes of PCM vs FM PPM
a few zillion notes ago and would like to add some fuel to that
fire.

Here is the problem.

If you have a electronic speed control that cuts power if it looses
the input pulse and if you fly with PCM you may die.

If you put that same speed control in a FM PPM radio you will
survive.

==========================================================================

I had a PCM receiver in my Thermic Charger and replaced it with
a PPM.  I had a servo driving a micro switch and replaced it with
an Astro proportional speed control.  I also replaced the Leasure
motor with an Astro Cobalt 05.

At the 495th fun fly this weekend I flew it this way for the first time.
I did a (cheap) range test on the ground but I didn't run the motor
too much cause I didn't want to run down the motor battery too far.

Anyway on climb out after it got up about 100 to 150 feet the motor
started cutting out.  Sounded like a car that started missing.

So what was wrong.  Well I never had much confidence on the motor
capacitor because of the way I had to rip it out of the Astro wiring
harness and put it in my harness.  I may easily have damaged it physically
or with heat when I soldered it back in.

Anyway with the extra noise from the motor it would swamp the receiver.
Since the FM doesn't have a "Hold Last" like my PCM does it the motor
control would cut the power to the motor.  As soon as it did the motor
would stop making RF noise and the receiver would again supply a pulse
out to the motor controller and the motor would kick back in again.

So what did I do - I just throttled back and didn't climb anymore.

I thought about this a lot and at first thought about putting my
PCM back in.  Figuring that it would definitely not allow the motor
to cut out.  But having second thought I realized that the FM PPM
was doing me a favor and letting me know I had a motor RF problem.
Further more if I had been foolish enough to put the PCM in it could
be fatal because.

With the PCM receiver when the motor started generating RF noise
and as I get far from the antenna the PCM would go into failsafe.
On the throttle this would be "Hold Last" and it could continue to 
generate RF noise and keep the radio in failsafe.  The other
channels would lock to Hold last and you could then watch the plane
go away or into the ground.  At best it would accidentally fly closer
to me and the receiver would then pick a strong enough signal to come
out of failsafe.

For what it's worth the failure would be the same for a FM PPM if it
was driving a servo and micro switch.  In the absence of a RF signal
the receiver doesn't put out servo positioning pulses and the
servos stay (depending in the brand receiver) put.

========================================================================
Summary

If you use an electronic speed control Then
    If you have a PCM radio Then
		If you do not have throttle failsafe Then
            Use a FM PPM receiver in this plane
        Else
		    Program your throttle for full off under failsafe
        End If
    End If
End If


Kay R. Fisher
Who thinks PCM will be great when they do error detection AND CORRECTION
on a PER CHANNEL basis.

    Both my Futaba PCM's have throttle failsafe. The El'cheapo Conquest PCM
    sets throttle back to idle. The 1024 PCM has an adjustable throttle
    position at failsafe. I thought That all PCM's killed throttle when
    overwhelmed with garbage.   Gee Kay, your lucky that the silly PPM RX
    did not give you full down elevator with a twist of rudder, otherwise
    you may have been casulty #4 of the day. 
    
    Anyway, this just applies to Kay's situation. One can argue that if
    your in a dive when failsafe kicks in that you would have been better
    with PPM.
    
    
    							Dave
    
    
    PS: A little thought to keep the topic hot!
    

I received my new Airtronics MD7P from Tower last nite.  It's
sure a beaut, and it weighs a ton compared to my old 5LK Futaba.

However, instead of getting the new -102 servos with the radio, I
was surprised to see the -631 servos.  Actually, based on Kay's
recent experience with servo hysteresis, I'm not too broken up
about it all, but I thought that I should look into the matter
further just to be sure.

First, I called Airtronics and talked to Jack Albrecht.  He said
that they are ending manufacturing on the MD7P, and that they are
shipping them all out with the 631s.  We talked a little about
the receiver, since if it contained the 631s it could have been
sitting on the shelf awhile.  But when I went home to check it,
I had the latest 92785 receiver and the current number
transmitter module.  This is important because the older MD7Ps
were shipped with the pre-AMA certification receiver which would
not pass.  These are listed in MA.

But, as a side effect of having the new receiver (actually an
8-channel) the channel matching between the Tx and Rx is screwed
up.  They give you a little paper to show the correspondence:

Tx Channel	Rx Channel	Function
  1		4		Throttle
  2		2		Aileron
  3		3		Elevator
  4		7		Rudder
  5		1		Retract
  6		6		Flap
  7		5		Aux 1

Kind of a bother, but I can live with it.  

Jack said that they would be able to maintain the MD7P with
on-hand parts and with compatible parts from current radios.

I called Tower to see if I could get a better price because of
the older servos, but they said that I must send the radio back
to get credit.  Since I know that the radio doesn't come with the
102s, I'd be wasting my time.  so there it sits.

I also had a problem with the OS .40, but I will enter a note on
that under the proper heading on Monday.

John, et al,

For what its worth:

I put my Cub back together Friday night, and just out of curiosity did a quick
and dirty check of the servos. Just eyeballing things 1 click of the trim levers
produced discernable movement on all surfaces and throttle and return to center
was sufficiently quick and accurate.

These are well used servo's, having been through a lot. The radio was a VG4R
transmitter and receiver. 

Randy

P.S. This is the Cub that was for sale. Its not anymore. Oh yeah, Saturday was
great flying weather here in the Springs.

    I just noticed in MA that Futaba's AM stuff and old single conversion
    5 channel PCM has made the list. Interesting stuff. Tends to suggest
    that AMA testing is fine to a point. I know for a fact that my 5
    channel conquest PCM gets nailed by the TV4/chan 20 problem. Still
    seems like a safe bet is to find an RX on the AMA list, then of those
    choose a dual conversion RX.
    
    
    							Dave
    

Dave,

   Do you mean the non-narrow band single-conversion AM Attack versions made it 
or something else (Conquest?)?

    The newer attack series made the grade. The Old AM conquest stuff did
    not as expected. The old Conquest 5 channel PCM did pass.
    
    
    							Dave
    

    Does anyone know for sure if the same crystals are used in AM and FM
    sets??
    
    When I called Futaba, they said yes, the same crystals are used. 
    On the flip side, both AM and FM crystal sets are listed in the 
    catalogs...  Is this another example of Futaba marketing prowness
    or is there really a difference??
    
    thanks,
    jeff

    Jeff,
    	It probably depends on the design.  Dual conversion receivers have
    two crystals.  They are not the same as single conversion ones.
    
    
    Charlie
    

    Phew... I made through all 118 replies. I was all set to order
    an attack 4 ch/glider (s133 servos). Actually I did order it
    but I can still return it. Cost is very important but I don't want
    to buy junk. I am building an elektra UHU sailplane (electric).
    I chose the attack becuase of price and "glider" package. But it
    sounds like a Airtronics $/6 channel FM vangaurd would be a much safer
    bet. My only concern is weight/size of reciever and servos for an electric
    sailplane. I'm convinced that airtronics would be better because
    they seem to worry more about the customer (meets AMA, upgrades,
    price). Futaba owners are probably happy now but they sure had to sweat
    it out for a while. Waiting for MA list, upgrades etc. I understand
    the vision sounds like the ideal radio for a sailplane but I don't
    have those kind of $$$.
    
    

                BACKGROUND  INFO  FOR  RADIO  DECISIONS
                ---------------------------------------


    This is the first of a series of articles to help you understand how
    radios work and how to critically read the manufacturer's literature on
    their products, knowledge you need to make intelligent decisions about
    radios.  I have tried to write it for a beginner in the hobby with the
    assumption that the beginner does not have a technical background.  It
    doesn't cover the basics that the beginner needs to know to build and
    use a plane; the focus here is on the radio purchase decision.


Basic concepts for a starting point:
------------------------------------

    In the following note I will explain some RC fundamentals:  what is
    "bandwidth", single and double "conversion", and the basis for several
    types of interference.  I will do this without using any advanced
    mathematics, but in turn you will have to accept a few concepts on
    faith:  1) that radio energy can go through empty space (That one was
    easy.), 2) that something called "frequency" is a parameter of radio
    energy (Another easy one!), and a third concept involving distortion
    that I will describe in a moment.

    We know that the AC power we use for our household appliances is also
    called "60 cycle power" or "60 cycle voltage".  An engineer would say
    that the frequency of this power is "60 cycles" or "60 cycles per
    second".  The modern phrase is "60 Hertz", but it doesn't matter; these
    phrases all mean the same thing, and the words are not important to us. 
    The concept of frequency as a measurable parameter is important.  

    The same concept of frequency is applied to radio energy, but the
    numbers are very different.  It says on my radio transmitter that the
    frequency is "72.430 MHz".  The notation, "MHz", is shorthand for
    "millions of Hertz".  Yup, the numbers sure are different, 60 Hertz
    versus 72,430,000 Hertz.  And it happens that this is why one form of
    energy stays in the household wiring and the other form goes through
    space.

    Now one of the radios on my bench is at 72.430 MHz, and the other is at
    72.390 MHz.  So "frequency" is a parameter (of the radio energy
    transmitted  through space) that is apt to be different from one radio
    to another, and that allows one radio receiver to listen to a
    particular transmitter while another receiver is listening to its own
    transmitter.  In short, radio **frequency** is the thing that differs
    that allows two of us to fly at the same time at the same field.

        Channel numbers are simply another level of shorthand.  If you know
        your channel number, you can look up the frequency in a table.

    Before we move on to the third concept, let's talk about stereo music
    systems.  If we turn the volume up high, there is a point where it
    starts to sound awful --- not merely loud, but of awful quality.  That
    is because something in the system is getting overloaded and distorting
    the electrical signals inside the system.  It happens that our radio 
    receivers have several distorting circuits deliberately included in the
    design; they couldn't work without them.  And sometimes the distorting
    devices should not be there.  In a later article on 3IM I'll talk about 
    the good guy and the bad guy distorting devices.

    Now for the third concept to be taken on faith:  3) when two streams 
    of radio energy of different frequencies go into a distorting device,
    more than two frequencies come out.  The output will include energy at
    the frequency difference of the inputs, energy at the sum of the
    frequencies, and usually the two input frequencies as well.  

        You don't believe this magic?  Sure you can.  You see magic every
        day.  If I mix yellow paint and blue paint in a bucket, the paint
        in the bucket will be green.  Now THAT is magic.  The concepts are
        not the same or even related, but take it on faith that if I mix
        72.710 MHz energy with 72.750 MHz energy in a distorting device
        then some of the energy will be converted to 0.040 MHz energy.

    In a radio receiver, the [usually deliberately] distorting device that
    converts energy from one frequency to another is called a mixer, and it
    does something called conversion.  We will come back to this later.

Bandwidths and filters --- narrow, wide, and whatever:
------------------------------------------------------

    Bandwidth is an easier concept.  But first, let's talk about gravel and
    sand and sieves.

    If I take a sieve made of window screening and fill it with sand, the
    very fine particles of sand will fall through the screening.  Sand
    particles of all sizes went into the sieve; fine sand came out.  I
    might be ridiculed at a sand pit, but I'd like to call this sieve a
    fine-sand-passing-filter.  It stopped the coarse sand particles, so I'd
    also like to call it a coarse-sand-stopping-filter.  

    Radio designers have similar phrases.  If a device passes high
    frequency radio energy, it is called a "high pass filter".  There are
    devices that pass only low frequency energy, and these are called "low
    pass filters".  "High" and "low" are relative terms here --- the
    borderline number between high and low might be a number like 150,000,000 
    or 18,000, etc.  What is important is that there are devices that can
    separate out different frequencies in an input stream, and these
    devices are called filters.

    Let's go back to playing with sand and gravel.  After the fine sand has
    fallen through the screening, almost all the sand left behind is
    coarse.  Let's put that remaining sand into a different sieve made with
    1/4 x 1/4 hardware cloth.  Now more sand falls through this sieve.  The
    sand falling through is bigger than the holes in the screening and
    smaller than the holes in the hardware cloth.  We have selected sand
    within a certain size range.  The analogous radio device is called a
    "band pass filter"; it passes energy between two frequencies.  The
    frequency difference is called the filter's bandwidth.

    The size range of the sand passing through my combination of sieves is
    a characteristic of the sieve system.  It is also a characteristic of
    the sand that passes.   One phrase, two things being characterized. 
    Likewise, the word, "bandwidth", applies to the filter and to the
    energy that it passes.

    Sieves and filters aren't perfect.  A percentage of the very fine sand
    will not find its way to the screening and will remain in the "output".
    Some needle-shaped particles of sand will pass through even though they
    are really large pieces.  Radio filters also have fuzzy boundaries, not
    perfectly sharp edges.  If there is enough energy just barely beyond
    the edge, some of it will get through.  This is an important concept.

Radio designs --- single and double conversion receivers:
---------------------------------------------------------

    Now let's use these concepts and talk about RC radio receivers.

    The transmitter puts information about the stick positions onto a
    stream of very high frequency radio energy and sends that energy
    outside via the antenna.  It happens that the transmission contains
    radio energy at many frequencies, but for a moment let's just consider
    a single frequency, the one on the label on the transmitter.

    The receiver has the task of selecting this energy from all the other
    radio frequencies in the air at that moment.  The question is "How does
    it do it?"  It starts by grabbing some passing energy with the antenna
    (Now, *THAT* is magic!) and bringing it into the circuitry.  But the
    antenna isn't very selective --- sort of one-size-fits-all, from RC
    channel 11 through RC channel 60 without changing antennas.  The next
    thing in the circuitry isn't much better.  A circuit called an "RF
    amplifier" increases the energy level and does some filtering, but it
    isn't yet sufficient to separate out nearby RC channels and pagers
    because the percentage difference in their frequencies is extremely
    tight.  For example, my channel 32 radio transmits at 72.430 MHz, and
    the adjacent pagers are only 0.010 MHz (or "10 kHz") away; 10/72430 is
    very, very tight!  Can you imagine trying to build a sand filter that
    could differentiate between grains of sand differing in diameter by so
    little, only one part in seven thousand?  Separating, for example, a
    grain 0.125000 in diameter from a grain 0.125017 in diameter.  The
    radio designer has a difficult problem. It would be a lot easier if the
    task were to separate frequencies differing by, say, one part in 50,
    and that is exactly what the radio circuit will do.  And it does it
    with a mixer.

    Remember that if we put two frequencies into a distorting device called
    a mixer then energy at the difference frequency will come out.  If the
    receiver generates some energy of its own locally at 72.885 MHz and
    mixes that with my transmitted energy at 72.430, then the difference
    frequency will be 0.455 MHz.  The pager frequencies will be shifted to
    0.445 and 0.465, still only 10 kHz away, but the percentage difference
    is now about 2%, a lot easier to filter in something called an
    "intermediate frequency amplifier" (an "IF stage").  Now that the other
    junk has been separated out, the stick position information in my
    transmission can be extracted, but that's a discussion for next month.

    What I have just described is a single conversion receiver.  The
    desired incoming energy was converted to energy at a much lower
    frequency and then put through a band-pass filter.  The IF frequency is
    usually, but not necessarily, at 455 kHz because commercial components
    are readily available at 455 kHz.  There is otherwise nothing magic
    about the number 455.  I could build a single conversion receiver with
    an IF of 789.123 kHz if I wanted to.  However, most receivers in use
    today work just this way with a single IF at 455.  (Figure 1)

    How does my Futaba Attack receiver on channel 32 differ from yours on
    channel 30?  We know that a little black thing called a crystal makes
    all the difference.  Guess what is used to generate that local energy
    at 72.885 MHz that was used to convert the 72.430 down to 0.455?  If I
    wanted to receive channel 30 at 72.390, I would have used a different
    crystal to generate 72.845 and convert the 72.390 to 0.455.  So that's
    what the crystals are for --- to generate a "local oscillator" ("LO")
    frequency just 0.455 MHz above or below the desired RF frequency.

    "Above or below", he said!  "Above" we understand; what's this "below"
    stuff?  Well, it doesn't matter whether the frequency difference is
    positive or negative; it is only the numeric difference that counts. 
    And that leads us to one of the shortcomings of the simple receiver
    just described.  The desired 72.430 differs from the 72.885 LO by 0.455
    MHz, but so does 72.885 + 0.455 = 73.340.  This undesired 73.340 energy
    would be equally acceptable to the mixer and is called the "image"
    because it is sort of a mirror image of my frequency about the LO
    frequency.  (Figure 2)  One of the purposes of the RF filter before the
    mixer is to reject this unwanted image.  One measure of a receiver's
    goodness is the "image rejection ratio", a topic for another day.  

    The image will always be at twice the IF frequency away from the
    desired  channel.  When the IF is at 455 kHz, the image will be 910 kHz
    or 45.5 RC channels away.  You haven't yet heard much about this
    because none of the pre-1991 channels had images near another pre-1991
    channel.  That will change, and the situation is exacerbated if there
    are pagers or certain TV channels nearby.  The situation is further
    complicated for you by the freedom of the radio designer to put the
    local oscillator either above or below the desired RC channel; that
    puts the image either below or above that channel.  The radio
    documentation never bothers to say which it is for a particular
    receiver; most people never ask.  It does matter.  In the case of an RC
    channel 12 receiver, 910 kHz away is either a pager between RC channels
    57 and 58 or it is the picture for TV channel 4.  If I were planning to
    fly RC12 near a TV4 transmitter tower, I'd want to know where my image
    was if my receiver was a single conversion model.

    Notice that the designer for this channel 12 receiver has a difficult
    choice with no "right" answer once RC channel 58 is on the market.  If
    the IF is at 455 kHz, both choices for the LO are "wrong".  The
    solution is to put the image further away by having a higher IF.  But
    the reason for the low IF was to get better filtering, better
    "selectivity".  Fortunately, there is an answer to this dilemma.

    This leads us to double-conversion receivers.  The Airtronics Vanguard
    receiver uses 10.7 MHz for the first of two IF stages.  That puts the
    image 21.4 MHz away, a separation rather easy for the RF filter to
    reject, so the "image rejection" of the Vanguard is very, very good. 
    But an IF of 10.7 doesn't do a whole lot of good for the percentage
    filtering problem, the "selectivity", so they follow the first IF with
    another mixer and a second IF at a much lower frequency.  It happens
    that the second IF is at the usual 455 kHz, but most of the problems of
    the single-conversion system have been solved by the combination of
    these two conversions.  (Figure 3)

        In particular, the "TV4/RC20 problem" and the "23 channel
        separation problem" have been solved.  You may not have heard about
        the "23 channel problem" yet, but you will in 1991.  If you and two
        friends are flying on three different frequencies, and they are
        using radios that differ from each other by 23 channels, you can
        get hit no matter what frequency you are on.  Their transmissions
        act like local oscillators for each other in your first mixer and
        generate 460 kHz.  If your IF is at 455 kHz, that is too close, and
        some of the interference energy will get through.  (Remember the
        fuzzy edges of real filters and real transmissions.)  The "TV4/RC20
        problem", a "22 channel separation problem", and a "22.5 channel
        pager problem" are all similar.  And all are potential causes of
        crashes if your first IF is at 455 kHz, even if your receiver is
        narrow band. An IF at 10.7 MHz rejects this interference easily, so
        double conversion receivers don't have any of these problems.

    So now that the differences between single and double conversion
    receivers are understood, how about the differences between narrow and
    wide band receivers.  It is possible for a single conversion receiver
    to be as narrow band as a double conversion receiver; both do the
    critical filtering in the 455 kHz IF stage.  The number of conversions
    has little to do with the receiver bandwidth.


Bandwidth --- narrow, wide, and fuzzy:
--------------------------------------

    You recall that the transmitter puts information about the stick
    positions onto a stream of very high frequency radio energy and sends
    that energy outside via the antenna.  In the case of an "FM"
    transmitter, it encodes this information by making very, very tiny
    changes in the frequency of the transmission and, for reasons that I
    won't get into this month, it keeps making these tiny changes
    incessantly about a thousand times a second.  It's a busy little
    bugger.  The bandwidth of the transmission depends upon the size of the
    frequency change, the rate at which it makes these changes, and some
    other magic.  An "AM" transmission has a similar bandwidth, but you
    probably don't want to ask me why.  

    So the desired stream of energy contains radio energy at many
    frequencies, not just a single one, and these many frequencies are
    mostly clustered in a band called the transmitter bandwidth.  My
    channel 32, gold stickered transmitter emits energy between 72.425 MHz
    and 72.435 MHz. The transmitter bandwidth is about 0.010 MHz or 10 kHz. 
    I say, "about", because the edges of the band are fuzzy, not sharp.  In
    all of history there has never been a frequency band with absolutely
    sharp edges; they are always fuzzy.  So are the filters.  Some filters
    such as "crystal filters" are more sharp than others, but they are all
    fuzzy to some extent.  This is an important concept, because it
    explains why a filter will pass at least some energy outside its band;
    the amount passed will depend upon the fuzziness of the filter and the
    fuzziness and strength of the energy presented to it.

    This concept of filter fuzziness is expressed graphically as a plot of
    the filter's willingness to pass a single presented frequency as a
    function of that frequency.  You have probably seen such graphs in the
    advertisements of Airtronics or in articles in our magazines.  The
    graphs often have the shape of a Halloween ghost --- a narrow, rounded
    top with sides called, "skirts", that slope outward.  The steeper the
    sides, the sharper the filter; the wider the top, the wider the filter's
    bandwidth.  But beware of any freedom exercised by advertising artists;
    they exercise lots of artistic license in their drawings.  Note also
    that if the sides slope, the determination of the width is also open to
    interpretation.  These graphs are usually drawn in units called "dB"
    (Don't ask.) that start at zero at the top and become more negative as
    you go out on the slopes.  A more negative dB number means a greater
    rejection of the associated frequency.  So the bandwidth is properly
    expressed as a width at a particular "dB down" --- "down" because "dB"
    is always relative to some reference, in this case the maximum for the
    filter.  Some advertising wording will take advantage of this freedom.

    The same measurement in dB is used to express the spread of radio
    energy, in which case the measurement is in relative strength at a
    particular frequency.  The FCC requirement for our transmitters is
    that their emissions be -35 dB [relative to the maximum] at 20 kHz
    from the center frequency.  The AMA guidelines for gold stickered
    transmitters is that they be 55 dB down at +/- 20 kHz, so the AMA is
    being much more strict.

    How does this apply to reading a manufacturer's description of his
    product?  Let's look at some recent literature.  The AMA guidelines for
    narrow band receivers is that the rejection be 60 dB or better at +/-
    8.5 kHz.  This statement is an elaboration of the simple "10 kHz"
    bandwidth requirement; it states how severe the rejection should be
    near the edge of the band.  The Airtronics advertisements state that
    their #92765 receiver is "better than -65 dB at +/- 8 kHz."  Now -65 dB
    is better rejection than -60, and if it is -65 dB at 8 kHz, it will
    almost certainly be even more severe at 8.5 kHz from the center.  So
    the Airtronics receiver is much better than the AMA guideline.  The JR
    manual for their X-347 system states that the selectivity of
    their #NER-627XZ receiver is "8 KHz/50 dB".  How does this compare to
    the AMA guideline?  It isn't clear.  The rejection at 8.5 kHz will be
    better than the rejection at 8.0, so the "50 dB" number will be better;
    it may or may not be 60 dB.  They claim to meet the AMA guideline, so I
    would conclude that they just barely meet it; they certainly don't
    claim anything better.  The Futaba literature in my possession is more
    cryptic; it doesn't give any such numbers.  

    For the last year or so there has been another problem in reading the
    advertising copy.  Your transmitter's bandwidth is probably *not* the
    same as your receiver's bandwidth, and that is OK.  But the term,
    "Narrow Band!", in an advertisement possibly referred only to the
    transmitter.  An excessively wide receiver will be dead meat in the
    coming years as more pager-type services come on the air and as more
    people discover the low entry prices of modern radios and ARF's.

What have we covered and what is to come?
-----------------------------------------

    Now you understand single and double conversion and why double is good
    for you.  You understand that narrow band'ness is a separate issue; you
    already knew that narrow'ness is goodness.  (In a future article we
    will talk about limitations on this.)  And you know why using channel 20
    near a TV channel 4 transmitter is worse than having bad breath. 

    Next month we will summarize the different types of interference and
    discuss 3IM in particular.  After that we will complete this guide to
    reading advertisements by discussing AM, FM, and PCM and by dissecting
    some current ads.

    Your comments and suggestions are invited.

                                                    Alton Ryder, 12/31/90

    

    Figure 1            A Single Conversion Receiver


        |
        |
        |       +----------+   +-------+   +-----------+   +--------------+
        |       |          |   |       |   | 455 kHz   |   | Demodulation |
        +-------+ RF stage +---+ Mixer +---+ IF filter +---+ Decoding and |
    Antenna     |          |   |       |   |           |   | Distribution |
                +----------+   +---+---+   +-----------+   +--------------+
                                   |
                         +---------+----------+
                         | Crystal Controlled |
                         | Local Oscillator   |
                         +--------------------+






    Figure 2            The Image Dilemma For A Single Conversion Receiver

    V       V                           V       V      VVV           
    |       |                           |       |       |            
                                     Desired  Local   Image           
           IF                         RC 12   Oscil.   at                       
    0     .455               (66-72) 72.030  72.485  72.940          (76-82)
                              TV 4                   =pager           TV 5

                                                 72.930 72.950   
                                                 RC 57   RC 58 




    Figure 3            A Double Conversion Receiver


        |
        |
        |   +----+  +-------+ +-----------+   +-------+ +-----------+  +-------+
        |   |    |  |       | | 10.7 MHz  |   |       | | 455 kHz   |  | the   |
        +---+ RF +--+ Mixer +-+ IF filter +---+ Mixer +-+ IF filter +--+ other |
    Antenna |    |  |       | |           |   |       | |           |  | stuff |
            +----+  +---+---+ +-----------+   +---+---+ +-----------+  +-------+
                        |                         |
              +---------+----------+    +---------+----------+
              | Crystal Controlled |    | 11.155 or 10.245   |
              | Local Oscillator   |    | Local Oscillator   |   
              +--------------------+    +--------------------+

    Hello,
    
       I was planning on buying the ARISTO-CRAFT 455 CHALLENGER.
    
    Does anyone have any reasons why I should not buy this RADIO.
    
    I am getting it for $94.95 at America's Hobby Center in NYC.
    
    Any advice will be appreciated.
    
                       Thank You;;;;;;
    
          _Colin
                        

>           <<< Note 51.121 by HPSTEK::CPLUMMER "Outlaw Gravity !!" >>>
>                     -< ARISTO-CRAFT 455 Recommendations >-
>
>    Hello,
>    
>       I was planning on buying the ARISTO-CRAFT 455 CHALLENGER.
>    Does anyone have any reasons why I should not buy this RADIO.
>    
>    I am getting it for $94.95 at America's Hobby Center in NYC.

Colin - give us a hint - what is the proposed use of this radio.
If it is on a surface frequency (for cars and boats only) then I
think nobody would find fault with it.  If you intend to use
it for airplane use then there are a few reasons why you may
want to reconsider your choice - as follows:

1.  I am not familiar with the Aristo-Craft models.  I assume the
    455 Challenger is a 4 channel FM.  If it is there are competitively
    priced models available from larger more reputable vendors such as
    (Alphabetical order) ACE, Airtronics, Futaba, and JR.

2.  No Aristo-Craft radios are in the AMA 1991 Equipment certification
    list.  Neither are any ACE radios but they have a long standing
    reputation for being sound investments.

3.  Do yourself a favor and whatever you get make sure that the Transmitter
    comes with a gold sticker (1991 narrow banded) and the receiver
    is either a dual conversion or a JR ABC&W.

My advice is - spend a few dollars more and get an Airtronics, Futaba,
or JR.  Also move up to 6 channels.  You may never use the extra channels
but this usually also brings other features in the package - such as
dual rates and some mixing capability.

I have only ordered one thing from AMC and was satisfied.  My only
complaint is that they do not accept charge cards - only COD or
prepaid.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################
                        

Yeah, Kay's right.  That radio was made by a subcontractor in
Korea who fabricated it to World's standards.  World wanted a
cheap radio, and that's what they made.  Unfortunately, in
today's environment there's only one word for that radio:
obsolete. 

I think the World radio has the gold sticker, but don't get
suckered in, the real test of a 1991 radio is in the receiver,
and I don't think that receiver has AMA approval -- the minimum
requirement for a 1991 radio.

I go through this because its the same factory that is now making
the hot RCD receivers and servos -- different set of standards,
far better equipment.  The servos on the Challenger radio are
very bad compared to ones from Airtronics or even (ugh) Futaba.

Of course, if you aren't flying planes, you can disregard the
above advice, since the reqirements for boats and cars are far
less critical.  However, even in that area, the major
manufacturers make better equipment.  Pick up an RCM or a Tower
catalog and look at the 4 channel gear advertised there -- and 6
channel is even better.  For another $20 or so you should be able
to get a better radio.

There's a number of these pre-1991 radios being advertised
nowadays. I've mainly seen them advertised by America's, but even
Tower is trying to palm them off.  The trick is to look for the
words: AMA approved; don't buy junk, it will get you in deep
sushi very quickly.  I know, I'm a sucker for junk engines.

    Thanks for the advice.....   I think I will see about buying
    an AIRTRONICS.  I am planning on using this radio for an airplane.
    
                             _Colin

    For a six channel radio you not only get 2 more channels
    you get the dual rates (as kay pointed out) and more servo's !!!
    You almost get the 2 channels for free by buying the extra servo's !!!

>>  I was planning on buying the ARISTO-CRAFT 455 CHALLENGER.
>>  Does anyone have any reasons why I should not buy this RADIO.

    1.	It may have been a different model receiver being reviewed, but to
        quote George Steiner in the March RCM, "It was glitch city all over
        the place. ...... The adjacent channel rejection is practically
        non-existent to an AM signal and the 3IM receiver threshold level
        is the real culprit to its failure. ..... resembles a poorly
        designed AM system of fifteen years ago."

    2.	The designation may be coincidence, but the number 455 is the same
    	as the typical IF [in kiloHertz] of a single conversion receiver.

    Companies can improve, but I would not fly an ARISTO-CRAFT receiver in
    a plane if you gave it to me FREE.  A "bargain" ARISTO-CRAFT would be
    especially suspect.

    As everyone said here, there are no Bargain radios out there.  It is
    worth the $$$ to buy the best radio system you can afford if you are
    serious about this hobby.
    
    Charlie