[Elecraft] K3: 30M signal

[Jim Brown]

On Tue, 24 Mar 2009 14:42:02 -0700 (PDT), WILLIS COOKE wrote:

>From that I would suspect that it originates in my computer or 
>possibly router.

Ethernet terminals (computers, routers, switches, hubs) are well 
known to generate interfering carriers on 30M, 20M, 15M, 10M, and 
6M. The clocks are local to each system, so if you have neighbors, 
it's common to hear a cluster of them around 14,029, 21,052, and 
the low end of both 10M CW and 6M. Most, but not all, of the 
signal is radiated common mode by the Ethernet cable. Some of it 
is also radiated by wiring internal to the Ethernet terminal due 
to lousy shielding. 

The common mode part (nearly always a lot stronger than the 
internal wiring) can be attenuated a LOT by winding 4-7 turns of 
the Ethernet cable around a 2.4-inch toroid of Fair-Rite #43 or #
31 material. For long cables (more than about 1/4 wavelength), you 
will need a choke at each end of the cable. Each cable attached to 
the Ethernet hardware is capable of radiating the signal, so it 
may need a choke. Linksys products are well known to produce a lot 
of this trash. 

If you hear more than one of these carriers, kill power to your 
Ethernet router, switch, or hub to see which of those carriers 
goes away. That's the only one that you'll be able to choke 
(unless you are on really good terms with your neighbors). Now, 
restore power to it and apply the chokes while you listen to the 
strength of that carrier. 

More info on this in http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim Brown K9YC