Thanks Jim, I'll give it a read and order up some mix-31 toroids. Does it surprise you the KAT500 is getting power cycled as I described? Is it really that sensitive? 10 of the ferrite beads I got from DXStore (rated for 150MHz or lower) work fine for 10m-20m. But no dice on 40m, so I guess the frequency is just too low for them to be effective (or perhaps I'd need like 50 of the suckers!)
-Jeff On Saturday, February 14, 2015 10:06 AM, Jim Brown <j...@audiosystemsgroup.com> wrote: On Sat,2/14/2015 9:48 AM, Jeff Hall, W6UX wrote: > can anyone suggest some further experiments to try? Yes. The problem is that ferrite beads slipped onto a transmission line does NOT make an effective common mode choke. Those beads are inductive, and, depending on the length of the line and the operating frequency, many lines look capacitive. The inductance resonates with the capacitance, and the common mode current increases. To be effective as a common mode choke, we need a high value of common mode impedance, and the best way to get there is with a high value of RESISTANCE. We obtain that by forming a low-Q parallel resonant circuit -- we wind multiple turns of the feedline through a lossy ferrite toroid or clamp-on. The number of turns needed depends on the ferrite material and the operating frequency. The best ferrite material for the HF bands is Fair-Rite #31, because it has the lowest effective Q over the widest frequency range. Study k9yc.com/RFI-Ham.pdf and use the Cookbook as a guide to wind the chokes you need. The chokes are most effective at the feedpoint of your antennas. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to w...@ymail.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
