Funny that this should be mentioned, as I was about to post a message about
computer and stereo interference with a neighbor of mine. For years they
have never complained.. They were away for three weeks in January, and and
came over a week ago Sunday saying that since they returned they were
hearing something on their computer and stereo speakers. Based on the times,
it coincides with my beam aimed over their house.
I am going to try some chokes, and feel that this may help with the stereo,
but the computer speakers are aanother matter. I've printed out copies of
some pages that the ARRL has, including what was the booklet that the FCC
used to make available; primarily to help them understand that the problem
is with their equipment.
Does anyone know if the chokes available from Radio Shack are any better
than the ones available from say, MFJ? Would it be better to order some
Ferrite Cores from Palomar Engineers or Amidon?
dale - KB5IY
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "RFI List" <rfi@contesting.com>; <ik2dzn@astorri.it>
Sent: Monday, March 05, 2007 9:43 AM
Subject: Re: [RFI] HIGH POWER and RFI...
> On Mon, 5 Mar 2007 14:41:13 +0100, Claudio Astorri wrote:
>
>>He wanted kindly to inform me that on his computer's speakers and on the
>>phone he could listen to me (not so loudly.) all weekend long.
>
> It is VERY important that you make you neighbor understand that THIS is
> the cause of his problem, not your station. He would have the same
> problem if he lived near any other transmitter, like a broadcast station.
>
> Both of these product types are very cheaply made, and are well known to
> have poor rejection of RF. They usually suffer from all of the following
> problems:
>
> 1) They are unshielded (in plastic boxes), so the internal wiring acts as
> an antenna to receive your signal.
>
> 2) They lack RF filtering on their signal wiring, so that signal wiring
> acts as a receiving antenna.
>
> 3) They have "pin 1 problems," which also causes their wiring to act as
> receiving antennas.
>
> 4) Every semiconductor junction in the box can function as an RF
> detector.
>
> RF gets into equipment by a COMBINATION of these mechanisms. Some may be
> stronger than others. You may fix one and still have some RFI from one of
> the others.
>
> A US company called K-Com sells a very effective filter for telephones.
> You can find them on the internet. They come with US-style connectors
> (like Ethernet connectors, but 4 contacts).
>
> You can fix problem #3 with BIG ferrite chokes. See my tutorial for
> detailed advice.
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
> The only fix for problem #1 is the bucket treatment. Fill a bucket with
> water. Put the speakers in two times. Take them out once.
>
> 73,
>
> Jim Brown K9YC
>
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