[RFI] Computer birdies

charlie@thegallos.com charlie at thegallos.com
Tue Jun 26 11:49:49 PDT 2012

I personally found, with my router and computers that the computer was the really bad end, but putting cores on both ends helped too, as there was some low level stuff coming from the router

Sent from my phone, please excuse any mistakes
73 de KG2V

----- Reply message -----
From: "Steve" <steve65 at suddenlink.net>
To: <rfi at contesting.com>
Subject: [RFI] Computer birdies
Date: Tue, Jun 26, 2012 2:11 pm

Thank you Jim. I happen to have a few #31 cores, 2.4in OD. At the 
computer end of the ethernet cable I began threading the cable through 
the core and made some observations along the way as I measured the 
birdie at 14015KHz on the S meter of my ICOM IC-7800:
turns 0,    S-meter reading    S 8.5
turns 1,    S-meter reading    S 8.5
turns 2,    S-meter reading    S 7.5
turns 3,    S-meter reading    S6
turns 4,    S-meter reading    S4
turns 5,    S-meter reading    S2
turns 6,    S-meter reading    S2
turns 7,    S-meter reading    S1
turns 8,    S-meter reading    no S-meter movement, barely audible

There appears to be a similar reduction in birdie level on the other 
bands. The birdies are not gone but they are now at a level I can live 
with. Wonder if I could get away from them completely by installing a 
wireless card in the Dell Inspirion?

Out of curiosity I switched the cable ends and found that putting the 8 
turns at the router raised the S-meter reading from no movement to S7. 
Evidently the computer is the source of the birdies. So I switched the 
cable back to having the 8 turns at the computer.

A second #31 core with 5 turns at the router made no discernible 
difference in either S-meter reading or to my ear.


Steve K8JQ

On 6/26/2012 10:24 AM, Jim Brown wrote:
> On 6/26/2012 7:16 AM, Steve wrote:
>> Anyone ran into this kind of thing before? Advice as to how to rid
>> myself of these unwanted signals?
> It's the Ethernet stuff related to the router. The cables are acting as
> transmitting antennas, your ham antennas are receiving the noise.  The
> solution is multi-turn ferrite chokes on each of those cables. Five
> turns on a #43 or #31 core will make a nice dent in the noise.  See
> http://audiosystemsgroup.com/RFI-Ham.pdf  for details, and for part
> numbers and vendors for suitable ferrite cores.  EVERY cable can radiate
> the noise, including the power cables, so every cable should be choked.
> 73, Jim Brown K9YC
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