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 _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
