[Elecraft] 14.03 MHz Continuous Tone/Carrier?@#$

[Jim Brown]

On Tue, 14 Aug 2007 23:52:04 -0700, Leigh L. Klotz, Jr. wrote:

>I've asked a number of ethernet luminaries to explain to me the source 
>of the birdies, and gotten blanks.

That's probably because they're digital guys, not RF guys. :) They should 
attend one of Henry Ott's excellent classes on EMC. 

There is either a clock or a component of the Ethernet signal that is 
coupled as a common mode current to the Ethernet cable. That cable acts 
as an antenna, and radiates it, and we pick it up on our receiving 
antennas. The Ethernet transmitter and receiver SHOULD be perfectly 
balanced with respect to impedance, but it is not. It is that imbalance 
that causes the radiation. 

I've never found an Ethernet device that doesn't have this problem. From 
a practical point of view, the most effective fixes are to either turn 
them off or stick ferrite chokes on the wires to prevent common mode 
current. Even when you've done that effectively, you may still hear 
radiation from the internal wiring of Ethernet devices that are badly 
shielded and have large internal ground loops. 

73,

Jim Brown K9YC