[TriLUG] Television & RF interference -- yes computer related -- I think

[Joseph Mack NA3T]

On Wed, 6 Mar 2013, James Jones wrote:

> A Friend asked for me to help trouble shoot their church 
> video problems. They video recorded their sermon on a Mac 
> from a video switcher through several pieces of equipment 
> to their mac. All their monitors had clear pictures of the 
> video, but the Mac had a beat pattern in the video.

did the recording have the beat, or just the monitor on the 
Mac?

> The beat pattern would show for a couple of minutes, then 
> clear up for a few and then back again. I am thinking it 
> might be walkie talkies, handhelds or some nearby rf 
> communication center of some sort. Since it happens only 
> on Sunday morning and not during their Wednesday evening 
> service, I believe it might be a ham operator, cb'er, etc.

this could be a bit of work to track down.

First thing you need to know is that at the request of the 
electronics industry, the Regan administration removed the 
requirement that consumer devices have RFI and TVI filters 
on them. As a result you'll see notices on consumer 
electronics saying "this device must accept all 
interference". This saves the industry about 50c/device and 
lets the consumer (you) handle the problem. The rest of the 
world didn't fall into line with the USA, at least 
initially, so the devices shipped elsewhere, still had the 
filters. I don't know what the situation is now. I expect 
Germany will still require them, even if no-one else does.

> Need any and every thought on troubleshooting this problem.

first thing you can find is whether the interference is 
coming over the wires or through the air.

wires: wind the cables around ferrite cores, or put ferrite 
blocks around the wires (you can get them at Radio Shack). 
If it works you're done. If it doesn't work, the signal 
still could be come over the wires. If it's coming over the 
wires, change the wiring (if you can) to see if it makes any 
difference. You might have to change the order of devices.

air: put a metal cage around (and under) the Mac. Expanded 
Al mesh would do it. You can fold it over a table edge to 
make a box and lid.

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
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