On Sun, 18 Apr 2010 19:00:19 -0400, Bill Coleman wrote: >I found that putting a snap-on ferrite core around the power cord reduced >the spur to an S5 indication. A similar reduction could be had by placing
>snap-on ferrite around the power output leads. Study my tutorial on RFI and ferrites. http://audiosystemsgroup.com/RFI-Ham.pdf Most snap-on ferrites are designed for maximum effectiveness in the 150 MHz range. ANY "snap-on" ferrite is next to useless on 160M unless multiple turns are wound around it. If the wiring in question is radiating the trash as a common mode signal, you need enough turns around a ferrite core to place the very low-Q resonance of the ferrite choke near the frequency of the noise. This takes AT LEAST 10 turns through a relatively large #31 ferrite core. I've successfully used some moderately horrific cheap switchers in my ham shack by putting good chokes on both input and output cables, and by adding RF capacitors across both the AC line and the DC line. You can also suppress differential noise from SMALL levels of DC current with a choke on only one conductor. High levels of DC current will saturate a choke on only one conductor, but most of us don't worry a lot about RX noise when we're transmitting. :) Another point. It has LONG been known that twisted pair wiring minimizes the radiation and pickup of noise, yet we use parallel wire cable ("zip cord") for power wiring in our ham shacks. That's plain stupid if we care about noise and RF pickup! The problem is finding twisted pair cables of suitable size. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
