[Elecraft] KAT100 Problem

[Mike Harris]

G'day,

For info, my KAT100 may have developed an odd problem which I am
investigating:

1.  Antenna, 40 metre inverted "V" co-ax fed, native SWR 1.0:1 on 7050kHz.
This from day one with the KAT100 it could be matched on any frequency
I chose to try.  Sometimes needed a second pass of tune to make the final
match from 1.1:1 to 1.0:1.  Settings remained stable and the "1" led would
flash with modulation.

2.  During the CQ WPX SSB weekend it started suddenly showing  intermittent
high SWR (5:1) readings.  Switching to ant 2 which has the dummy load on it,
no problem.  Swapping the antenna to ant 2 seemed to resolve the problem.
Conclusion a problem with the change over relay.  Not so, the problem
returned and DC testing the relay showed OK.  On one occasion the led's
would indicate change over from ant 1 to 2 but no action from the relay.
After powering everything down and back up again normal action returned.

3.  During this SWR dance the KPA100 goes nuts as the load changes and
throttles back the power with lots of clicking of relays and flashing of the
display.  Probably the psu (SEC1223) can't handle the current and the
voltage goes low.

4.  Spent a lot of time troubleshooting the antenna and feeder.

5.  Connect the antenna directly to the K2 and no problem.  Via KAT100,
problems, SWR dances about the green range.  Switch the KAT100 to CAL mode
after matching the load and SWR remains as 1.0:1.  Switch back to AUTO and
the SWR starts to dance again.

6.  When running tune the KAT100 would seek a match, find 1.0:1 and then
continue to switch and settle on 1.1:1 - 1.3:1.  Will seek a match every
time pressing tune in high power and occasionally will sweep down from
red (5:1) to green (1:1) without any switching action.  Did a realignment of
the KAT100.

I don't think it is a problem with rf pickup on the control cable because it
has been tame since first switch on a few months ago.

Still digging and trying to understand the problem.

Regards,

Mike VP8NO (IOTA SA-002)
GQRP 10148
K2/100 #1400