Conference vmszoo::rc

The pupose of range checking is to test your transmitter/receiver
combination to be sure they are functioning properly. It is done with
the transmitter antenna fully collapsed or removed (read your radio
instructions), and walking away from your airplane while wiggling the
controls until control response stops or becomes intermittent. That
distance should be 50 to 75 feet (again, see your radio manual). This
simulates 1/4 to 1/2 mile distance with the transmitter antenna fully
extended.

Your first range check can be with the engine off. I have sometimes
attached a clothes pin to the elevator to give better visibility, and
then walk away while moving the elevator up and down. Alternatively,
have somebody stand with your plane and holler at you. This is best
done in your yard before you even go to the flying field. If you don't
get the required range, check your installation. It's likely that your
batteries are weak, your receiver antenna is broken (it can be broken
inside the plastic covering) or you have an intermittent connection
somewhere.

Before flying, you should perform a range check with the engine
running (and somebody holding onto your plane securely). You should
test it at idle and full throttle. It is possible for the engine
vibration to cause intermittent behavior in your receiver, which is
why the engine-running test is important. 

The best test is with the airplane pointing straight toward or away
from the transmitter. This will make the receiver antenna
approximately end-on to the transmitter, which is the worst-case
situation (and which is often the orientation during flight,
especially during the critical take-off and landing). Remember pit
courtesy and be careful of propwash. 

Don't even THINK of doing a range check with the motor running without
somebody holding onto the plane (the purpose of a range check is to
walk until your transmitter no longer controls the plane, which could
cause any behavior including full throttle). 

I agree with the notion that you should perform the range check
periodically, not just on a new installation. You should remember
the approximate range you got on your first check, and if that
range gets shorter by any appreciable amount (several feet or more)
you should not fly until you find out what changed. Remember to
keep the airplane and transmitter orientation the same when you
do this - the range will be quite different with the plane pointed
toward you vs. broadside. If you don't do it every flying session
(frankly, I know few people who do, although it's a good idea)
be sure to range check after every crash (including hard landings),
and anytime your touch your receiver installation.

If the range check fails and you can't diagnose and solve your
problem, do not fly. Period. Send your radio back to the manufacturer
for a complete checkout. This is a pain, but there can be no
compromising with safety in this case. Being a few weeks without flyig
is better than a demolished airplane or a personal injury due. You'll
probably find somebody in your club who has a spare radio they will
loan you until you get yours fixed.

Dave

    
    Hmmm...
    
    Can't find a better place for this, so here goes:
    
    Firstly yes I KNOW you're supposed to range check before EVERY session
    (or flight?). I do with new models, or after heavy arrivals.
    
    Yesterday was a superb day for flying, so the field was pretty busy
    (Wednesday evening is our only weekday slot at this field). I flew my
    'plane around, having fun and noticing the odd glitch. There was
    nothing really serious, and it could have been "bad thumb". Suddenly I
    lost all control. Frantic stick twiddling was getting me nothing, and
    my plane was in a spiral dive. I shouted my frequency, and ran towards
    the plane (good tips those, thanks whoever it was that "noted" them!)
    
    I gradually got control back as I got closer to the plane, and managed
    to get her back for a landing. Then I did the range check.... I could
    get nearly 6 feet before the reciever went ape! 
    
    Other people were also having trouble so we went and got the club
    scanner, which showed nothing, and the TX frequency checker, which
    showed everybody within tolerances. 
    
    I borrowed another TX, and changed crystals, with no effect. I also
    tried another RX battery. The gear is HI-TEC, so it's not the world's
    most expensive/advanced stuff! 
    
    Later in the evening, when things had quietened down I tried a range
    check again, and found it was good! I could get 70-80 feet with the
    aerial down, and control was rock steady. I tried a few flights, and
    had absolutely no trouble at all.
    
    No one else at the field has a TX on channel 71.
    
    So, what the heck happened? And more importantly what do I do about it?
    I'm not comfortable using this gear if problems can come and go without
    explanation! Any ideas, as always, gratefully received.
    
    Cheers
    
    Nigel.
    
    PS> The "consolation" was that my last landing was an absolute
    g-r-e-a-s-e-r!
    
                                                                         

Just went through this myself this spring. It was on an RCD 535 Rx (same as 
Hitec). Seems there are two crystals in the Rx. One that you plug in and a 
reference one that is soldered to the board. In my case it was the one 
soldered to the board that had cracked. Sounds like this might be a similar 
problem in your case. The other thing I checked which proved ok was a 
continuity check of the antenna. A broken or yanked loose antenna might 
cause it as well. Have you crashed this Rx recently? Could you have snagged 
the antenna and stretched the wire a bit?

    Do the range check with the motor running. Walk a few feet, bring it up
    to full throttle, walk a little further out and go to full throttle
    again, etc. This could point out a vibration problem.
    
    Also, if the receiver is accessible, say with the wing off, you can try
    a normal range check and have someone tap on the receiver while your
    doing it. This will also show if you have a problem that vibration
    brings on.
    
    Steve

    
    I did the range check with the motor running, and it seemed to make no
    difference. I also wiggled the RX aerial about during the checks, it
    was hard to be sure, but it didn't seem to make any difference. When I
    was touching the aerial I got jittering, but this could be down to my
    earthing it couldn't it? 
    
    I have crashed this RX (I crash EVERYTHING! 8^) ) but that was a while
    back, and it's been OK on quite a few flights since. I'll take a look
    inside the casing for any obvious problems.
    
    Thanks
    
    Nigel
    

    
    Oops!
    
    Sorry Jim, I meant to ask, was the crystal damage you had visible, or
    was it found some other way?
    
    Did you return the RX for service?
    
    Thanks
    
    Nigel
    

No, the crystal damage wasn't visible. I sent it in TWICE for service before 
they found it so it isn't even obvious on the bench.

If you open the case, do an end to end antenna check. This is something 
simple that you can replace yourself (exact length replacement)

I actually did a range check after the crash and mine seemed ok as well. I 
flew this Rx slope soaring down the Cape with just a little interference 
which I put off to the windy conditions. It wasn't until I noticed some 
significant problems with range in my HLG that I finally did an real, antenna 
down range check and could 6' range (I had about 150' with it up which is how 
I survived the Cape).

    
>    Other people were also having trouble so we went and got the club
>    scanner, which showed nothing, and the TX frequency checker, which
>    showed everybody within tolerances. 



  Could it have been 2IM or 3IM?  

    
    I've read about this problem, but I have to admit I just don't
    understand it! There were a LOT of transmitters on the field (the peg
    board was damn' near full!), as I understand it this could be a
    situation where it's likely to happen?
    
    Certainly the "recovery" happened after the field quietened down, so
    maybe there's a problem here.
    
    Anyone have any ideas how I'd check?
    
    Cheers
    
    Nigel.
    
    

The problem would be seen as "ghost" Txs on channels not operating. It's 
basically caused by harmonics from the other Txs

    Ah!
    
    Snag here was that we were checking for "outside" interference, so the
    scanner checks were done with all TX's off. The guy who "minds" our
    scanner had forgotten to charge it, so we only had time for one sweep. 
    
    I'll see if I get any recurrence, and check my channel if it happens
    again. I've checked the RX aerial, and tried tapping it with no
    problems. Maybe I should tap it with a club hammer........
    
    Cheers
    
    Nigel
    

Except in the UK 8^)

Nigel... Looking for warheads for your rockets for nexttime? 8^)

    
    Now there's an idea....... I could strap the TX to a nice big rocket,
    launch it and then wait to see how long before the servos on my plane
    start to jitter. It'd sure save all that walking..... 8^)
    
    Jim, what's "Except in the UK" ? (decent weather probably!).
    
    Nigel who's_still_not_convinced_he_should_buy_a_rocket!
    

Jim C. was commenting on the 1991-ness of the US environment. I wasn't 
sure how much of that applied over there in the UK.

Maybe an AstroBlaster or a Phoenix RCBG? 8^)

    It's probably 2 im or 3 im.  I've had problems with my Challenger
    radio. It is a FM Dual conversion Design. But, the older receiver was
    very marginal with other transmitters on the field in particular,
    Futaba. I would routinely get stepped on when someone turned on their
    channel 46 transmitter. I eventually bought a newer style reciever on
    Channel 16 and still got hit somewhat but not often enough to worry
    about it. 
    
    
    					Steve M...

>Jim C. was commenting on the 1991-ness of the US environment. I wasn't 
>sure how much of that applied over there in the UK.


  Boy your fast!!!  I saw that I'd had a notes collision with Nigel and 
deleted my note.  Your probably the only one who saw it.

  But yes...I had mentioned that *most* of the systems we buy here in the
US are '1991' rated and reject 2IM interference.  The Futaba Attack is a
notable exception to that rule.  It's narrow band (1991 compliant) but does
not have dual conversion (or ABC&W - gotta keep the Evl-1 happy) to filter 
out the 2IM.  

    Here goes. Simple definitions.
    
    3IM - an unwanted RC equipment generated signal that is caused by 
    	  three operators of RC TX's standing too close together and who 
    	  are equally spaced apart.
    
    			e.g RC22   RC30     RC38
    
    			or  RC29   RC32	    RC35
    	  
    	  In the first case they are 8 RC channels apart, and in the
    	  second case 3 RC channels apart. Any set of equal spacings can
    	  cause this situation. That is why pilots stations are spaced out
          about 20' in most clubs. If the operators stand too close to each
    	  other they can Intermodulate! and shoot each other down. 
    
    	  It is easy to remember this as interference that is at the TX
    	  end and is spoiling the transmission.  
    
    
    2IM - an unwanted RC or other generated signal only caused by two RC TX's 
    	  operating 23 RC channels apart. This is not a distance issue. It is 
    	  a frequency spacing issue brought on by the addition of odd numbered
    	  channels. (23 channel spacing can only occur if odd and even numbered
    	  channels are operated together)
    
    
    			e.g. RC30   RC53
    
    			or   RC11   RC34 (RC 57 would also be a problem)
    
     			or   RC20   TV Channel 4 sound
    
    	Whenever two frequencies are 23 channels apart 2IM will happen.
        
    	The frequncy that is generated can affect ALL 72 mhz RC receivers 
    	regardless of what specific frequency they are on.
    	
    	This is not a big deal if you have a receiver that can reject the
        unwanted 2-IM signal.
    
     It is a weak signal, after all, and if you have dual conversion or JR ABC 
     you will never know that it is there.
    
    The problem manifests itself when your RX cannot reject the unwanted 2IM 
    interference. I have tested several 1991 approved RX's and one of them 
    failed everytime. The Futaba, I forget the number, RJ112? something...,
    
    If we all have receivers that can reject 2IM there is no problem. If we
    all stand 20' apart there is no problem on 72mhz.
    
    There is no cure for 1-IM. That is when somebody operates exactly on
    your frequency.
    
    Hope this helps.
    
    E.
     

    
    Thanks for the "plain man's guide" Eric!
    
    One more question, do 3IM and 2IM present a problem in the 35MHz band
    too? 
    
    Thanks again
    
    Nigel

    Only if the RX's are built to the lousy spec that was applied here!.
    
    BTW. I still have a bunch of 35mhz radios. I wonder what they are using
    35 for out here?. :-)
    
    
    E.

    
    35 MHz is a NAVY frequency, used on some boats (don't remember the exact 
    purpose). Was not a problem in Colorado, might be a problem in New England.
    
    Bernd

    I finally fixed my landing gear and ended up finding this problem while
    trying to test the gear operation.  What I did was simple: I plugged in
    my retract servo, turned on the reciever and then turned on my Tx.  I
    got no response.  I flicked the Rx on and off a few times to check if the
    servos were getting power.  They were.  Strange I thought.  So i
    extended my atenna.  Now I got intermittent response.  Worked best with 
    the atennaes next to eachother.  Hmmm.  I changed my TX program to
    control the gremlin.  The gremlin worked fine with the TX atenna
    collapsed.  I cycle US60 RX battery and repeat.  Still on response. 
    Any ideas?  I haven't done anything to the plane since the last pattern
    contest except fix the gear.  It's a little chilly in my basement, but
    not enough to screw up the Rx I would think.  Help!!!
    
    andy
     

Are the two Rxs the same modulation? Cold could drain the batteries. If you're
trying to run a PCM Rx with a PPM Tx, you'll get no response. Could the crash
have yanked the Rx antenna and broken it? Or a crystal?

    My US60 Rx is PCM and my gremlin is FM (or PPM).  THey both worked
    before.  I know it's not the batteries, I just cycled them.  It must be
    the antenna or the crystal...Antenna is easy to check, but the crystal
    is not.  Does anyone know if I can swap a crystal from one of my FM
    receivers into my PCM receiver?
    
    andy
    

If they are both the same brand (JR) you can. The RF boards are the same, it's
the pulse train encoding/decoding that is different.

    Ok, I'll give that a try.  I have one spare FM Rx that I can switch the
    crystals with.  Hopefully that is the problem.  I don't feel much like
    soldering on an antenna.  Thanks...
    

    PS (Jim) - I installed Red Hat Linux on my machine at home...works
    great!
    

    Geeze, Andy, it'd be hard to believe that "crash" (really too strong a
    word in this case) screwed up the receiver/ant/crystal - it was just a
    little bitty "balloon and thunk" on the gear struts. Unless the
    receiver broke loose and slammed against something hard...
    
    Couldn't a dead cell sneak by a cycler?
    

    No, the cycler reported 850 mAh on the battery. Kind of hard to do that
    with a dead cell.  Like I said, the servos did move when it was close
    enough.   I also tested the battery voltage with my multimeter.  I
    can't remember if I tested the plane at all since the crash either.  It
    ould be the antenna.  I remember stepping on it many times and almost
    yanking it out. 
    

    Do you have a set of wire stretchers in your flight box? If it was down
    to a few strands due to that, it wouldn't take much to finish it off.
    
    Congrats on the Red Hat. Lamar just got a Pentium 100 and booted up
    Slackware on it.

    Contrary to what you OBVIOUSLY  believe, constantly stepping on the
    RX antenna wire is NOT condusive to long airplane life. 8^)
    
    Take the 4 little screws out of the RX case and take it appart. Check
    the antenna connection. Put your throttle stick all the way up and
    wiggle the antenna wire and see what the throttle servo does.

And it's not a secure holddown when running up the engine.

I remember a time, years ago, when a friend fired up a Goldberg Falcon 56. It
was made stock with the stab put on with rubber bands as well. Running up the
engine with the stab against the ankles wasn't the right technique 8^)

    Well, I went home and changed crytsals in my Rx and now it works. 
    Now, where can I get replacement crystals and how much do they cost?
    
    andy
    

They are specific to the manufacturer. Bob at R/C Buyers should either have it
in stock or be able to order it. He will mailorder it to you.

I hear he has a neighbor DW that's always in there 8^)

    RC Buyers has crystals..  Call first to make sure they have the 
    channel/make/model that you need.
    
    Cost??  Less than crashing your plane!  :-)  I haven't looked lately,
    but I suspect around $10...
    
    Cheers,
    jeff
    

    Make sure it wasn't just loose.
    
    S.

Yeah, I'd say to put the old one in the one you stole the good crystal from
and see if the problem follows it. It could be a cracked PC board that was
reseated with the crystal insertion 8^(