Roger saith: "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."
Ouch! That indicates that whoever laid out the board had no idea that 'gapping' the board is a BAD IDEA(tm). Please, whoever was responsible for laying out the I/O board for the P3, go to this site, and learn what REALLY has to be done to properly design PC boards for EMC: http://www.learnemc.com/index.html I attended a whirlwind 4-hour course on automotive EMC at last year's Freescale Technology Forum that was a very compressed version of the 2-day courses shown on the LearnEMC home page, and it was a real eye-opener. If there is anything critical as a take away from that experience, it was that the PCB layout will make-or-break your EMC issues, and is the best and most cost-effective way to stop EMC issues, rather than trying to use ferrites, etc. after the fact, all of which will never be as effective. If you can't do the two-day course (highly recommended) there are free extensive tutorials to be found at the "EMC Tutorials" link on the main page: http://www.learnemc.com/EMC-Tutorials.html It's all good stuff, and should be mandatory learning for anyone laying out PC boards these days. 73, -- Dave, N8SBE > -------- Original Message -------- > Subject: Re: [Elecraft] P3 generates noise on 144MHz > From: "Roger Crofts" <[email protected]> > Date: Tue, February 12, 2013 6:02 pm > To: "elecraft reflector" <[email protected]> > > > 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:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ 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
