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Re: [RFI] KY filters?

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] KY filters?
From: "Jim Brown" <jimbrown.enteract@rcn.com>
Reply-to: Jim Brown <jimbrown.enteract@rcn.com>
Date: Fri, 19 Dec 2003 13:38:58 -0600
List-post: <mailto:rfi@contesting.com>
On Fri, 19 Dec 2003 17:35:41 +0000, Rob Atkinson, K5UJ wrote:

>some phone line filters.  I wanted to get a good one because I run QRO so I 
>picked up two KY filters.  Has anyone used them?  What were your results 
>with them?  

Don'[t even know what they are. But I do recommend wrapping the phone
line a as many turns as you can through one of the 2.4" diameter
toroids commonly used as a 1:1 balun at the input of antenna tuners.
Palomar and others sell them. Moreover, I suggest you stock up on
various toroids like these so you have them on hand for various
consumer gear that has problems. 

I've found it very common for RF to get into audio gear via the
loudspeaker wiring (typically it will back up to the input via the
feedback loop), so don't overlook it. Also, zip cord is MUCH worse in
this regard than any garden-variety twisted pair. I would change the
loudspeaker cable to twisted pairs before spending money on toroids. 

And remember that virtually all detection follows square law, so a 10
dB reduction in the RF level will generally result in a 20 dB reduction
in detected RF. Thus most RF solutions don't need to be perfect, they
simply need to pull the detected RF down into the noise. 

Jim Brown
Audio Systems Group, Inc.

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