I followed up on the RFI theory and quickly found a solution to the problem.
My TS-590S has a homebrew breakout box on the REMOTE connector. This breakout box provides key line level shift and key line interrupt for my SteppIR. The TS-590S ALC control line is on this cable but is not terminated in the breakout box. I disconnected the REMOTE connector from the TS-590S and arranged for direct local keying of the KPA500. This eliminated a possible path for RF entry to TS-590S (and also KAT500 and KPA500). In this configuration I was able to output over 400 W on 7.01 MHz with no oscillation present. With the breakout box connected oscillation was present with power greater that 108 W. I should be able to fix the problem with better decoupling and/or choking of the breakout box connections. Thanks to everyone for the suggestions and comments. 73, Andy, k3wyc ______________________________________________________________ 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
