One thought, have you run the Elecraft TX GAIN Calibration procedure recently? It's built in to the K3 Utility.
Unfortunately, the Utility sets the TX gain at a midpoint frequency on every band, frequencies I rarely use, and I was observing first dit "power spikes" in the output of the KPA1500 when driven by a K3. To eliminate these power spikes (thanks to Rene at Elecraft for this tip), with the amp. in STBY and the tuner enabled for best match on your favorite frequency (or if connected to a dummy load), set the drive power to exactly 50W and press and hold the XMIT button (TUNE), then once the display stabilizes, tap it again (just takes a few seconds). This re-calibrates the TX GAIN on that frequency, instead of the one used by the Utility. At any other power setting other than 50W, the TUNE button doesn't change anything, so change the power level back after you are done. You could do this once on you favorite areas of the CW bands, then use the K3 Utility to Save that configuration, then repeat the procedure on the phone segments, and use the K3 Utility to Restore whatever configuration you need that weekend (but this may not work so well for mixed mode contests). So try the simple 50W calibration test on 40m to see if it makes any improvement. As for KPA1500 output power variation with temperature, it is annoying, and it seems to vary from KPA1500 to KPA1500, perhaps depending on how many other devices or heat sources are located near the ventilation holes. The best option when operating a contest seems to be to set the KPA1500 minimum fan speed to 1, so that amplifier doesn't heat up too quickly, maintaining a more stable (but not perfectly stable) power output level. 73, Bob, N6TV On Sat, Aug 24, 2019 at 11:45 AM Jim McCook <w...@cox.net> wrote: > I'm using my K-3 with the KPA-1500 and have a problem with extreme > changes in power output with a given drive level on 40m CW. This > happens to a lesser extent on other bands with different antennas. My > 40m antenna is tuned to 7.025 where SWR is 1.1:1. On 7.000 it is 1.4:1 > and at 7.050 it's 1.3:1. Within that range of frequencies the output > _without_ the tuner at a given drive level (30w) varies from 1300w to > well over 1700w. Using careful _tuner_ settings it's only slightly > better. I have to reduce drive to 24 or 25w to get below 1500w, > depending on the temperature of the amplifier (power output varies a lot > with temperature changes). Higher temp = lower output. > > I have tried to compensate in the segments where output is excessive by > using manual settings via the Utility. This has helped slightly, but > still isn't adequate. I've resisted using ALC because of concern for > generating distortion. Having to ride the drive level from the K-3 is a > PIA, especially during contests. > > It seems to me a good answer would be to have higher input attenuation > so drive requirement would be higher, maybe around 70+ watts. I'd > expect changing drive level by the same number of watts (5 or 6) would > not affect output as much. I'd also assume the power output would not > vary nearly so much with a given drive level. > > Is this a possible solution? I've also understood that most > transmitters (even the K-3) have cleaner output near highest rated output. > > Help! > > Jim W6YA > > > ______________________________________________________________ > 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 n...@arrl.net ______________________________________________________________ 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
