[Elecraft] Unstable KXPA100 output on 40 Meters.

[John Nogatch]

On Sat, Jan 16, 2016 at 7:58 AM, Hans J Rasmusen OZ7BQ
<oz7bq at yahoo.dk> wrote:...
> The output and SWR green LED status indicators on my KX3 (sn 18xx) KXPA100/KXAT100 (sn 08xx) combo exhibit some unusual behavour on 40 Meters CW...
> The above problem appears to be RFI related, as the jumping output/SWR indications are present only when feeding an antenna. ...
> My questions are:Has anyone experienced anything similar?....

I experienced similar problems on 40m with my K3+KPA500+KAT500, i.e.
the SWR would suddenly jump, the amplifier would fault, and the
automatic band selector antenna switch would chatter. Because the
problem only seemed to occur on 40m, I investigated the antenna, found
a loose connection, but it did not fix the problem. Eventually,
similar fault occurred on 20m.

Finally, I found that the short coaxial cable between the KAT500 and
the antenna switch was intermittent. I could observe change in receive
signal strength when I twisted the cable, near the PL-259 connector.
Substituting a different cable has completely fixed the problem. I
suspect a bad soldered shield connection in the bad cable.

At one point, while investigating this problem, receive sensitivity on
40m only, was 30 dB worse, although transmit was normal. The RX_ANT
had been activated, and there was no receive antenna connected!

-John  AC6SL