Conference hydra::amiga_v1

In case my typo was confusing,
watching a video has NO video interference.  Only
broadcast reception is screwed up.

    Re .0:
    
>   Unfortunately, and perhaps because of the time it was made, my "Class
>   A" Amiga computing device really screws up television reception
>   thoughout the whole house.
    
    Obviously, it shouldn't do that.  (My A500 with all sorts of stuff
    connected hasn't been a problem.)
    
    Two questions:
    1.	What model (and vintage) Amiga do you have?
    2.	Since most emissions are at external connections, have you tried
    	to isolate the source?  You could start by disconnecting ALL the
    	ports, turning on the Amiga, and checking for interference.  Then
    	reintroduce one port at a time until interference is observed.

I've isolated two sources of the problem, in a brute force sort of way:

The CPU, as the only powered on device, causes a lot of interference.

and...

The external Supra 30 meg drive, as the only powered-on device,
also causes a lot of interference.  In fact, at the time I tested
these, one caused diagonal lines in one direction on the TV, and the
other device casued diagonal lines which crisscrossed the first set.
Just great.

Does this help?  If not, what further tests must I perform to isolate?

The amiga is a vintage 1985 A1000 machine.

I also have a two meg card.  THe CPU power test was run with the card
attached.

Dave

Oops, correction. One or other of the hard drive and cpu were one when
I turned on the other.  Turning on the second device only served
to compound the interference derived from the first.

I suppose I'd better test it again.  Is the remedy different for
hard drive interference than the remedy for CPU interference?

Dave

Are you using ribbon cables between any of the attached devices?  These
are often sources of interference.

-steve

    One possible source is that the slap-on-side devices are not properly
    grounded to the system so they are acting as an antenna.  I had that
    problem with an A1000/memory board, the tipoff was when I tried foil
    to cut down the RF - I ran it from the metal case of the memory board
    to the shield on the joystick port, suddenly the RF was greatly reduced.
    
    The solution was to get a more solid connection of the A1000's RF
    shield to the the memory board.  They were barely touching.
    
    Dave

Hmm.  re: .5

The Supradrive has an 18-24 inch ribbon cable which
connects it to the card hanging off of the bus. And..
I don't remember having the RF problems before the purchase
of the drive (four residences ago, 5 years ago).  But the
interference was never very bad after I bought the drive either,
until I moved to my current residence.  Now it has house-wide effects.
Still, maybe I'll try running the CPU without the drive and without
the ribbon attached.

If it *is* the ribbon, what do I do to shield it?

re: .6 

How do "improve this connection"?

>     The solution was to get a more solid connection of the A1000's RF
>     shield to the the memory board.  They were barely touching.

Thanks for your support!
(You don't get *this* in a NeXT conference ;)

Dave

    Check the position of your Amiga with respect to the TV antenna and
    lead-in wires.  You may be able to reduce the interference a lot by
    relocating your Amiga farther away from the TV wires.  Shielded TV
    wire should help, too.

    If you were not having problems at your previous residence, I would
    suggest you get the earthing checked out either in your house's
    electrical circuitry, or the TV antenna.

    You need to identify what's different. It's the same TV/computer,
    different house/power supply, and possibly a different TV antenna. Get
    everything that has changed checked out for correct electrical
    connections.

    Lindsay

    
    Something to keep in mind is the strength of your TV reception.
    If it's weak , it'll be much more suceptable to interference.
    Try leaving your Amiga switched on and realigning your TV antenna.
    
    Steve.

Well, lots of suggestions, and thanks.  Many don't apply
however (or won't help).  I'll ask my builder about
"earthing".  

as for:

- distance of amiga from TV's - they're at opposite ends of
  house already

- moving antenna - all channels get messed up, some more than
  others.  Moving antenna (which is only on set)
  just varies the condition, but doesn't fix it.
  Would adding an attic antenna fix it?  Or would the interference
  just be more detectable to the television?

I guess the real thing is still, "how do I shield the amiga",
once I identify the most likely points of emission on
the box and drive.  Someone mentioned foil?  Does foil
really work?  How much do I need?  Do you "ground" it?



Thanks for the input!

Dave

    Dave,
    	I suspect that your problem is your TV antenna. Even if you were 
    using it at tour previous location the signal strength where you are 
    now could be much weaker. I would suggest that an external antenna
    would be ideal but failing that an attic one should show an
    improvement.
    	Also, checkout the antenna plug connections at the TV. Make sure 
    all connections are solid. Soldered if required.
    	Hope this is of some help.
    
    			Paul
    

Since this occurred after a move, it would seem worthwhile to check the inside
of your Ami to see if the RF shielding has jarred loose in the move (unless you
hand-carried it in a box full of cotton balls). Could be that the transition is
the causative factor, not the new environment.

Bob

    Re .3:
    
I've isolated two sources of the problem, in a brute force sort of way:

>   The CPU, as the only powered on device, causes a lot of interference.
>   
>   and...
>   
>   The external Supra 30 meg drive, as the only powered-on device,
>   also causes a lot of interference.  In fact, at the time I tested
>   these, one caused diagonal lines in one direction on the TV, and the
>   other device casued diagonal lines which crisscrossed the first set.
>   Just great.
>   
>   Does this help?  If not, what further tests must I perform to isolate?
    
    Simply turning off components IS INSUFFICIENT to "isolate" them. 
    You must PHYSICALLY DISCONNECT EVERYTHING from the A1000 to test it. 
    Problems like this are caused by components acting as antennae.
    
    Given a reply that the Supra drive is connected using a ribbon cable,
    that's a likely suspect.  (It also makes me wonder how the Supra could
    receive FCC certification.)

	my Amiga has always interferred with the Tv.  I can see the image of the
	Amiga screen on the tv screen, so it's in the modulator section, but
	it's in color, and the 500 doesn't have color encoding, so that's odd.
	I used to deal with EMC on the job, but I havn't done anything about
	it at home.  I suspect that a neighbour lady bought a new tv  after
	I moved in because she thought her old one broke when it was just
	the amiga.  The FCC can shut down your computer if neighbours 
	are smart enough to complain.  You could try to pay for them to
	get basic cable tv.
	is your computer between the tv stations broadcast antennas and your tv?
	I concur that you should disconnect everything and reconnect one
	thing at a time.
	Mine interferes with nothing connected, but not as badly.
	The most susceptable channels for me are 2,4,5, which I think are
	around 50-80 MHz or so.
	Too bad we can't borrow the bubble in MRO and test some Amigas ;-)
tom

    Just to add another voice to the babble... :-)
    
    If you live more than, say, 20 miles from the center of Boston, and
    don't have a good TV antenna, you should expect problems like Dave
    Tenny is having.  Many of us live a few hundred feet or more above sea
    level and have a pretty good "radio horizon," with rabbit ears giving
    decent TV reception.  However, the signals are not all that strong. 
    Since the eye can perceive interference when the interfering signal
    strength is up to 50 dB below the desired video signal, 
    
    A good, directional antenna in the attic or on the roof will certainly
    improve reception because it provided more of the desired signal and
    moves the antenna farther away from the interference source. 
    Installing cable TV would help, too. :-)
    
    The "earthing" problem mentioned a few replies back is just grounding
    to earth ground.  It's possible that the third prong in some outlets
    does not provide a good connection to earth ground, making the Amiga's
    shielding less effective.
    
    Also, I agree that Dave should try disconnecting all the external
    peripherals to isolate the source of interference.  For what it's
    worth, my old A1000 with external floppies has never caused
    interference to the TV, so I suspect that cabling is the problem.
    
    Some other things to try... Connect the cabinets of the various units
    together with a hefty wire, making sure that the wire is connected to
    bare metal at both ends.  Also try wrapping the ribbon cable in foil. 
    If that reduces the interference or changes the effect, then there's
    your culprit.
    
    Wes
    sometime RF engineer

    
    Ref .15
    
    Tom,
    
    	You must have a verrrryyy very old A500 then cause mine has color
    encoding (PAL type of course).
    
    			Paul.
    

    Hi
    
    	Been read this and as stated previously grounding the unit as well
    as shielding are the main crouse for resolving this problem.  
    
    1: Connect a ground wire from each unit to the ground screw of your AC
    outlet (The center screw that holds on the faceplate covering the
    outlet.
    
    2: If you have ribbon cables assume they are not the shielding type.
    You can make own or shield the ones you have.  One way is to place the
    cable between two lenthgs of copper tape beind sure to get an ground
    connection on both ends.  (IE be sure the tape connects to the chasis
    of the two units that the cable runs to and from.
    
    The key to fixing this problem is to give a easy path for the energy to
    go to ground.  If not this energy will go off into free space just as
    if it a signal from a transmitting antenna.
    
    OThere tips are to keep your cables as short as possable.  You don't
    have to cut them just loop neatly any excess lengths.  EMI is a bear
    to track down. and do not assume that if you know what is causing the
    source of the energy, you know how it is leaving your system!  These
    eminations can just as easily travel down power lines thourghtout your
    house as to traveling torought free space. (eaiser as a matter of fact)
    
    I work at the NIO GSM TEMPEST lab and surpressing signals like this is
    what we do.  People in our groupe have gone baled trying to figure out
    how somthing gets out.
    
    Good luck
    
    George C.
    

THanks for all the replies.

If my Amiga cooperates (my Supra turned up on its back
with legs crossed again this weekend, a regular habit
for my particular Supra drive which I belive to the
core of my being is a piece of shit), I'll try some of
the suggestions here.

If/when I get around to fixing it, I'll post my experience
in reply to this topic for other luckless folks..

Dave

Well, I didn't have any copper tape, but I've done the following experiments,
obtained some results, and taken the following actions (none of which 
appear to help).

A) I ran the disk drive detached from anything else.
   - It messes up TV reception
B) I ran the CPU separate from everything but the monitor
   - It messes up TV reception too.
C) I tried running a ground wire from the socket faceplate screw
   to each of

   1) The memory card
   2) The Supra card
   3) The Supra drive
   4) 1 & 2 simultaneously
   
D) I tried wrapping the ribbon cable in Reynolds Wrap, and running
   running the ground to both it and the drive casing. (I didn't
   have any copper tape).

Overall, there appears to be little or no improvement from any of these
measures.   My speculation is that both the CPU and drive have always
been guilty of badly shielding emissions, and that the problem manifests
much more now because of my current TV reception area, antenna situation,
etc..

This is somewhat intuitively backed up by the fact that some channels
(like 2, 4, 9, 25, 37) get completely blasted from existence by the
computer devices, while others (5, 7) are only nominally affected, or
even not affected at all.

So I guess that's a wrap. Thanks for all your help.
Guess I'm stuck (maybe an attic Antenna will fix the problem,
I didn't have the problem in Harvard, which had terrible reception,
but I had an external antenna).

Dave

Yeah, I know, you said "it's a wrap," BUT...

Your comment about some stations being affected and others not gave rise to a
semi-weird idea- if the Amiga is directionally in the "line-of-sight" between
your TV and the affected stations, can you simply *move* it? If this does have
the (predicted?) effect of changing which stations are affected, you'd be
fairly confident that an attic antenna would indeed remove the problem.

Bob

    RE: .20  You find that those emissions disappear when you unplug the
    video cable from the back of the Amiga. Dunno why it is so nosiy, but
    that's been my experience.
    

	If you don't already have one, try one of the power strips that
    includes an RF trap.  It's possible that the noise is getting into the
    TV through the house wiring.

	If it is an old house or was not in some city or county zoning area, 
    the wiring may not be up to the standard in the electrical code. 
    Specifically, there may NOT be a ground wire to the various electrical
    outlets, especialy if they are the two prong type.
	If you are not comfortable poking around inside outlet boxes, you may
    want to have a professional do it for you.  The main problem is that you
    may find a serious problem and it will cost some real money to get it 
    fixed.  However, you should chalk the expense up to personal safety and
    'insurance' rather than 'fixing the TV' if you do find a wiring problem.

	It is important for safety to have good grounding, but it doesn't
	always help EMC.  Floating shields and groudned shields mostly just
	have opposite phases of reflection.
	Tom

>	It is important for safety to have good grounding, but it doesn't
>	always help EMC.  Floating shields and groudned shields mostly just
	^^^^^^
>	have opposite phases of reflection.

	True with the restriction stated, but several replies here have
    mentioned connecting to the 'metal screw in the center of the outlet' as
    an important part of the noise elimination process.  
	If that screw is not connected to earth ground, there is no hope of
    diverting the RF energy to a place where it will be disipated harmlessly. 
    (I'm not saying that an earth ground WILL help, only that the LACK of one
    can NOT help.)  
	In other words, checking the house wiring will not hurt and could be
    an important part of fixing the problem.  It is an important variable that
    has changed between the time when the problem was tolerable and the current
    situation.

	There has also been an assumption here that the problem is radiated RF
    noise.  You also need to check for CONDUCTED RF noise.  A power strip with
    an RF filter in it can help with that.

	The RF energy can be dissapated as heat in the skins of  a
	floating Faraday
	cage.  A resistive but conductive internal
	coating that matches the source impedance does this best.
	Tom