This group is outstanding. Thank you Bob K4TAX for taking what must have been a fair amount of time walking thru the consequences of a 40- or 60-Ohm mismatch. That radiation resistance graph you attached is one I have used for decades!
Thanks Don W3FPR as well. There are several connectors in between the amp and the dipole’s center insulator. Since we have had several temperature swings of late, I shall firm them up when the rain stops. I’ll keep plugging. My KPA500/KAT500 combo had its own set of characteristics that I eventually learned, but not a PA current out of bounds. That one is new. Thanks everyone else for contributing. 73, Gary W2CS > On Mar 15, 2019, at 5:10 PM, Don Wilhelm <donw...@embarqmail.com> wrote: > > Gary, > > Have you considered that there may be something in your antenna system that > is heating up or otherwise changing with the 1500 watts power? > The first thing I would suspect is a balun that is heating, or a connector > that is not quite tight enough. > > Those kind of problems will not show up at lower power, but at 1500 watts may > become troublesome. > > 73, > Don W3FPR > > On 3/15/2019 3:25 PM, Gary J Ferdinand wrote: >> I’m in the process of checking out my amp. I have two dipoles (40 and 80). >> At resonance both show a 1.2:1 SWR with ATU totally bypassed. With ATU on, >> it remains bypassed on 80, but shows only the ATU ON LED on 40. In both >> cases the resultant SWR is 1.2:1. SWR measurements are from the KPA1500 >> display. >> When I use the amp with my K3 and drive it up to 1500W, I am occasionally >> getting an excessive PA current fault at 63A. From a cold start it’s 60A, >> but as it warms up in contest usage I find the power drops off, so I have to >> adjust the K3 to bring it back up to 1500W. At that point the PA current >> goes over 60A. >> Interestingly, into a dummy load the 1500W point shows a PA current of only >> 55A. So the 1.2:1 SWR, be it via a bypassed ATU or using the ATU, is >> sufficient to raise the PA current eventually to excessive levels. ______________________________________________________________ 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
