[Elecraft] KXPA100 Intermittent VSWR Issues
Jack Brindle
jackbrindle at me.com
Mon Dec 8 00:19:29 EST 2014
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 at 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
>
>
>
>
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