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Re: [RFI] Electrostatic filter rfi

To: "RFI@contesting.com" <RFI@contesting.com>
Subject: Re: [RFI] Electrostatic filter rfi
From: "Jim Brown" <jim@audiosystemsgroup.com>
Reply-to: Jim Brown <jim@audiosystemsgroup.com>
Date: Mon, 28 Jun 2004 14:47:38 -0500
List-post: <mailto:rfi@contesting.com>
On Mon, 28 Jun 2004 13:29:54 -0400, Tom Berry wrote:

>The only solution I have been able to find is to turn them off.  I
>have tried coiling the power cord, beads on the power cord and I even
>tried plugging them into my computer UPS system which I think will
>isolate them from the AC line. 

Nothing you have described is likely to have any effect at all at HF. Assuming 
that the 
trash is getting onto the power line, you need far more serious filtering than 
you have 
described, and filtering that is specifically tailored to HF. Beads in general 
are useful 
only at VHF. 

A starting place for a common mode power line choke for 14-30 MHz would be 2-8 
turns around a 2.3" OD #43 toroid.  Power line filters such as those sold by 
can also help. For any of these filters to be effective, the equipment, the 
filter ground, 
and the outlet ground need to tied together at the frequencies of interest.  

BTW, don't just hang a filter and ground wire on this thing and call it a day. 
If the filter 
couples the noise onto a long ground wire, it can act like an antenna and 
radiate the 
noise. That's a good reason for having the series impedance to form a divider. 

For an example of this, have a look at 




This is the pole that services our former AT&T site at W6BX (see qrz.com). 
Something at the top of this pole is conducting HF noise onto the several 
leads, and every one of them is hot with the noise. I strongly suspect that it 
is the 
downleads (that is, the grounds), not the power lines, that are radiating the 

The fix, of course, is to eliminate the noise at the source.  

Jim Brown  K9YC

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