Check for something arcing in the antenna system at higher power. This would be something that heats up before the arcing starts, like maybe a grounding RF choke on a vertical or something similar. The worst feedline component for this is the cheap right-angle UHF adapter. The center conductors are not well made, and will bend and arc to the shell over time. This usually is a problem at powers higher than the KXPA puts out, but it can still happen.
We see a lot of these, and it is rarely something in the ATU, although that is a possibility. This is also _very_ difficult to track down since it is usually inside something in the antenna system and thus well hidden. You would be looking for the tell-tale signs of slightly charred or smoked markings. What are the antennas in use for both bands? - Jack B, W6FB > On Dec 7, 2014, at 7:07 PM, Jim Stahl via Elecraft <elecraft@mailman.qth.net> > wrote: > > I've run into several occasions where in mid-CW transmission my KXPA100 > (with internal tuner) SWR takes a momentary jump from matched to maybe 3:1. > I > see the SWR jump on both the KXPA front panel LEDs and on the KX3 VSWR > display. It lasts for maybe half a second, I hear several clicks of the > relays in the tuner, and them it's back to normal. When normal the SWR is > pretty > much 1:1 on the KX3, and the second green LED lit on the KX3. I've not > seen it happen at the start of a transmission, but rather several characters > into a CQ or exchange.. > > In the ARRL 160 contest Saturday night this was happening perhaps once > every 2-3 minutes. I'm using a fairly well matched antenna - not random > wires. > I also encountered this problem on 15 meters when operating from W1AW/8 in > WV in October. In both cases I was running a pretty high CW duty cycle > while running at a pretty good clip. The amp was warm, but the heat sink air > > flow is not blocked. > > Any thoughts? > > > 73 - Jim K8MR > > > > > ______________________________________________________________ > 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 jackbrin...@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 arch...@mail-archive.com
