Jump back down to Ron's input. I had that exact same scenario with my OCFD. As soon as I transmitted any length of time on CW above 250W the SWR would jump up and the KPA500 would fault. The problem was a too small torroid 4:1 balun. I bought a 5KW balun from Hy Power Antennas and the problem went away. Just because the balun is rated to 5KW doesn't mean you have to use that much power.
73, Rick W3BI -----Original Message----- From: [email protected] Sent: Monday, June 04, 2012 1:47 PM To: [email protected] Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down My bet will be on a bad connection someplace after the amp. With power something is shorting ... could be in coax connector, antenna, etc ... been through that. Once had found an elevated radial on 160 inverted "L" had dropped and touching a tree limb was the problem. 73, Mike -----Original Message----- From: Ron D'Eau Claire Sent: Monday, June 04, 2012 12:33 PM To: 'ai6ii' ; [email protected] Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down Mark has an excellent point, especially if you have a ferrite core transformer (balun, etc.) somewhere in the antenna system. One thing that can cause that behavior is heating of the toroid core. At a certain temperature, the core's magnetic properties change dramatically, changing the inductance and so causing the SWR to change. Ron AC7AC -----Original Message----- What happens when you run the KPA-500 into a dummy load? If all is well, I would guess that something is changing under high power and affecting the load. -----Original Message----- From: ai6ii <[email protected]> To: [email protected] Date: Mon, 4 Jun 2012 10:00:54 -0700 (PDT) Subject: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down I have installed a new antenna and have strange changing swr. When testing with RigExperts meter I find good resonance at say 15m (21.200). With the K3 at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I bring the amp online and drive it at 200 watts, all is still good even with a 15 second key down period. Driving the KPA500 to 275 watts, still okay with key down, although the KPA500 meter now shows 1.1. BUT when I increase the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500 shows REFL HI and drops into STBY. And here is the kicker...NOT ALL THE TIME! So I think it has to be in the coax. But the 75feet of RG213 is brand new premade from Cable Xperts with the connectors. I will try a different coax. Any other suggestions? ..mike ______________________________________________________________ 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 ______________________________________________________________ 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
