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To: "RFI List" <rfi@contesting.com>,"ik2dzn@astorri.it" <ik2dzn@astorri.it>
Subject: Re: [RFI] HIGH POWER and RFI...
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 05 Mar 2007 08:43:51 -0800
List-post: <mailto:rfi@contesting.com>
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 

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 

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. 


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.


Jim Brown K9YC

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