"Given its high duty cycle, you are asking for trouble if you operate your power amplifier in FT8 mode using your KPA1500 at anywhere near high power."
Worst case duty cycle on FT8 is never more than 50%. This assumes that you are transmitting every odd or even time slot. Very few stations are able to keep that rate for very long. So I would bet the actual duty cycle is more like 30% to 40% in actual use. On a practical note, I tried FT8 once in a contest (the first WWDigi contest). I ran SO2R, with each radio set to transmit on the alternate time slot. My station uses a single KPA1500 driven by two K3s, switched accordingly. I ran this setup for a whole day, and other than the fans getting to level 5 occasionally, it worked fine. I regularly use this setup on RTTY, and see similar results. I can run 2BISQ on RTTY without a problem. And to answer the original poster's question, yes, the amp will reduce output as it gets warmer. In my case it drops about 100 watts (1500 -> 1400) which is -0.3 dB. Hardly enough to worry about. Ken K6MR ________________________________ From: elecraft-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> on behalf of Kevin Robertson via Elecraft <elecraft@mailman.qth.net> Sent: Saturday, June 4, 2022 6:52 AM To: Rick NK7I <rick.n...@gmail.com> Cc: elecraft@mailman.qth.net <elecraft@mailman.qth.net> Subject: Re: [Elecraft] KPA1500 reduces power as it gets warmer? FT8 is a weak signal mode, designed for low power. Given its high duty cycle, you are asking for trouble if you operate your power amplifier in FT8 mode using your KPA1500 at anywhere near high power. I burned out my final on my K2 at 15 watts on FT8. 73, Kevin Robertson KD2WCY > On Jun 4, 2022, at 12:42 AM, Rick NK7I <rick.n...@gmail.com> wrote: > > Yes, the KPA1500 will drop 10% of the output, as it warms up. 1500 drops to > 1350, so you have to compensate with the drive. > > I'm told this is typical of all solid state finals (my KPA500 did likewise). > > If you're running the station remotely; bump up the fan speed to slow the > drop (or wear cans). > > 73, > Rick NK7I > >> On 6/3/2022 9:22 PM, David F. Reed wrote: >> I note my KPA1500 drops power at its temperature rises... >> >> Using FT8, so a relatively high duty cycle. >> >> Say I start at a heat sink temperature of 27 C, and 1,000 watts out; by the >> time the temperature is at 65 C, the power has dropped to 893 watts out. >> >> I have a couple of questions about this (not a complaint by the way): >> >> 1. Does anyone else experience this? >> 2. Is it normal? >> > ______________________________________________________________ > 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 kevin_robert...@me.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 k...@outlook.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
