Last night I cleaned all mating metal surfaces in the P3 but, alas, this made no difference. The noise was still at S6. When I had the I/O printed circuit board out of the case, I noticed that the earth planes for the power supply section and RS232 section are separated by a zig zag gap. They are commoned together towards the inner edge. This has the effect of lengthening the route of RF currents from the earthy side of C500 to the metal case. My thoughts are that C500 will do a great job of removing RF differential mode voltages across the power cord. It will not do such a good job of removing common mode RF voltages from the power cord. I believe it is the common mode RF voltages that are the problem. This was confirmed when I replaced the power cord with a coaxial one (as suggested by John, G4ZTR). This made no difference to the noise. I found a ferrite ring which was large enough to pass the power plug through it. In fact I passed the plug through it three times to form two tight turns and I moved this choke as close as possible to the P3 power socket. The result was that the noise dropped to S4. Almost there! I think it would be better if the filter was totally inside the P3 case. I will try that next.
Roger Crofts, VK4YB ______________________________________________________________ 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
