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Re: [RFI] Touch Lamp and 2m

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] Touch Lamp and 2m
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sun, 25 Dec 2005 11:55:14 -0600
List-post: <mailto:rfi@contesting.com>
On Sun, 25 Dec 2005 12:32:01 -0500, WA3GIN in Alex. City, VA 

>I found the touch light control box inside the china cabinet.
>Is there a fix?

I assume that something is connected by wires. The wire(s) will 
act as a an antenna, both receiving your transmitted RF and 
radiating noise from the controller. (We call it a power cord, but 
Mother Nature calls it an antenna). Both control wiring and power 
wiring will act as an antenna, and depending on how they are 
connected to the electronics, both can put RF into the 

Ferrite chokes surrounding those wires can reduce the antenna 
current. Look for ferrite parts that are just large enough in 
diameter to surround the wires, and about an inch long. It may 
take more than one part to provide enough impedance to reduce the 
current enough to solve your problem. Put the chokes as close as 
practical to the electronics. 

Ferrites are made with a broad range of chemical compositions, 
each with its own frequency range where it works best. Most clamp-
on ferrite parts that we see at hamfests are suitable for 
suppressing 2 meters. If you're buying parts, look for Fair-Rite #
43 material, or Stewart #28. 

RF is also coupled to the input terminals, and onto the circuit 
board (the traces act as antennas too). RF bypass caps can help 
this. You want small value caps with VERY short leads, and very 
close to the junctions that are detecting the RFI. 

There are tutorial app notes on my website about RFI and using 
ferrites for suppression. 

Jim Brown K9YC

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