When the KPA500 was keyed up, the K3 VSWR went from 1.2:1 to 1.0:1. Because the input circuit offered a j0 match, I concluded that the problem had to be associated with the amplifiers output. In bypass mode, the bypass relay connected the input directly to the output. I was confident that the Elecraft did their homework and the PA, PC board design was correct and offered a j0 match from the input to the output. I think the problem is on the ground side of the twisted pair. There's enough stray inductance to introduce loss between the PA board ground and the connector ground. There's no direct connection from the wire ground pin to the chassis. If my memory serves me, the only ground points on the PA board are on the corners of the board. On the input connection, there's a mini coax jumper.
Before changing it, I untwisted the wire about 4 turns and the VSWR went from 1.2:1 to 1.4:1. I twisted the wire tighter and it went back to the original measurement. When I worked at Argonne National labs, in the Avanced Photon Source RF group, we were working with 350 MHz, 1 megawatt klystrons. We learned all about ground loops the hard way. jack WA9FVP ----- Jack WA9FVP Sent from my TRS-80 :-) -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-KPA500-VSWR-on-6m-tp7610474p7610483.html Sent from the Elecraft mailing list archive at Nabble.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
