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

[Pete Soper]

Folks not interested in this subject should most definitely hit "delete" 
or "next" or something.

I think Rod and the earlier poster may be non-violently agreeing with 
each other that most consumer electronic equipment in this country is 
subject to FCC Part 15 rules and modern (with vanishingly rare homebrew) 
amateur radio equipment interference that is legally the amateur's fault 
is very rare, while US equipment is very susceptible.

IMO wireless microphones have zero chance of being a problem. 
Fergetaboutit.

But the FCC regs and your neighbors exist in two worlds. If you fire up 
1.5kw on 160 meters to see if you too can connect with somebody in 
Australia from here in North Carolina and your neighbor's house goes bat 
sh*t, it won't matter at all that all of their equipment is covered 
under FCC Part 15 and your equipment is perfect relative to part 97. 
Folks can sue other folks for a small filing fee, but long before that 
they can appear at your door, beet-red and implying that because your 
actions are interfering with their viewing of the (insert sports event 
here), you are the devil, but more to the point ask  *what are you going 
to do about it RIGHT NOW?* I'm speaking hypothetically now, but the 
short answer is if I'm holding onto my expected position in a contest 
I'll weigh the cost of telling the neighbor to go pound sand (while 
wondering just how bad it's going to be with my wife). But otherwise 
(and in all my experience in the real world, and everything I've heard 
or read about with my amateur friends, and because I never got seriously 
competitive), I STOP and then bend over backwards to help the neighbor 
eliminate their interference as soon as I can, even if it means I spend 
a lot of time in their home installing equipment I paid for.

To proceed I'm assuming this is about radio interference and not 
something correlated with the equipment in the church that is also only 
used at time X.

Amateurs do quite often tend to talk for a few minutes at a time. In 
contests talking for more than about 1 1/2 seconds at a time meant 
you're losing. :-) Morse code traffic can vary even more, from a 
fraction of a second bursts to long "rag chews."

RF overload is frequently the culprit, and so it doesn't matter if the 
nearby transmitter is squeaky clean from a spectral purity standpoint. 
If it's close enough, the receiving end has to have profound levels of 
bandpass filtering to avoid problems. Put a
different way, if you bring a transmitter close to a receiver and the 
transmitter is on frequency X and the receiver is on frequency Y, at 
some point Y is going to respond to X's signal and become unable to 
receive other signals on frequency Y and it *will* demodulate X's signal 
for many modulation types, putting crap downstream like video hash bars, 
buzzing, "Donald Duck imitations", etc.

Early on with my amateur hobby I was in a contest and there was another 
signal that was so incredibly loud I thought the person involved was 
obviously breaking one or more rules. But no, he was a few thousand feet 
away and I was pinning his signal strength meter too. Normal.

In my experience most often the interference gets into the neighbor's 
equipment via the  electrical wiring. Wrapping *all* of the power cords 
involved with their troubled equipment through ferrite cores can 
sometimes provide relief. You want to ask yourself "where are the long 
runs of wire here?" and create a very high (usually common mode) 
impedance at the frequency of interest. But what frequency is involved, 
and what kinds of common mode chokes (aka ferrites) are needed? The 
frequency involved and the ones that provide relief, of course. :-) And 
"long wiring" includes telephone wiring and home entertainment speaker 
wiring too. If I had a nickel for every time some non-linear component 
in a sound system rectified my SSB signal and put Donald Duck imitations 
into the speakers...

Using the blind shotgun approach, I have to say these filters below have 
been the best for me *for HF frequency interference* (HF is technically 
3-30mhz). If the problem is a UHF or VHF source, these might or might 
not be effective. More is better, if there is any overlap with respect 
to effective frequency. As a citizen I must apologize for the fact that 
after all this time Radio Shack doesn't publish the specs on these devices.

http://www.radioshack.com/product/index.jsp?productId=2103979&locale=en_US

There is of course a boat load of information on this subject available 
on the net. You might start here:

http://www.arrl.org/radio-frequency-interference-rfi

-Pete AD4L

On 03/06/2013 09:49 PM, R Radford wrote:
>> 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.
> Hmmm, that is not how I interpreted the action, and also does not seem
> to match up with what I read on the ARRL website.  In fact, the ARRL
> was one of the big proponents of the bill that basically states that
> as long as you are doing everything legal in your transmitter (ie: a
> ham radio operator), it is not your responsibility if it causes
> interference on another device. The FCC has the authority to
> investigate and go after noisy transmitters, but if the transmitters
> are operating within specification, there is no requirement that they
> must stop or change if it interferes with your equipment.
>
> This kinda makes sense to me as the old method would make each ham
> radio operator responsible for tracking down and fixing interference
> from their equipment, even if the fault was not in their equipment.
>
> A little discussion about it here:
>
> http://boards.straightdope.com/sdmb/showthread.php?t=85072
>
> And a good writeup on the ARRL site on their efforts to push the bill into law:
>
> http://www.arrl.org/bill-becomes-a-law