On Fri, 11 Sep 2009 18:21:40 +0100, David Cutter wrote: >I used a Honda on field day a few years ago, (240V mains outlet) and was >staggered by the amount of SMPS noise. I fitted a big filter grounded local >to the generator about 60ft away that made it tolerable.
VERY important point. "Ground" for a filter has NOTHING to do with EARTH. Rather, the 'ground" of the filter (its shielding enclosure) needs a zero length connection to the chassis of the noise source (the generator). You CAN tie this point to the earth, and it may help a bit, but it is the connection between the filter chassis and the generator chassis that is most important. BTW -- winding about 10 turns of the power cord around one or more toroids is also a very effective common mode filter for 2-10 MHz. Use fewer turns for the higher HF bands. See http://audiosystemsgroup.com/RFI-Ham.pdf for detailed winding guidelines and measured data for chokes. You should be able to get 10 turns of 14-3 cable through a 2.4-inch toroid. While you may want bigger conductors for the long run, you can certainly insert a short length of #14-3 at the generator without serious IR drop. An earth connection for the generator chassis can help here too. In both cases, the earth connection and the line cord through the choke form a current divider for RF current. The earth connection is typically on the order of a 50-100 ohms or so, and a big choke can be a few KOhms. 73, Jim Brown 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
