Hi,
The other night I left my K2/100 and KAT100 still attached to the
antenna, and we must have had a thunderstorm or the like pass through. I
had been using the rig before I hit the sack, and everything was fine, but
in the morning I got the dreaded "Hi Cur" warning if I tried to transmit
anything higher than 10w.
Subsequent testing proved the SWR bridge diodes in both the KPA100
*and* the KAT100 had changed from being diodes to short-circuits. A trip
to the local (dead loss) Electronics store to get some more 1N1755 diodes
produced 1 diode ! ( typical)
What's a bloke going to do with the Christmas postal rush in full swing and
Elecraft thousands of miles away?
In the end I replaced the 4 diodes with common old 1N4148's and everything
appears to be working fine......which brings me to the question......why
are the 1N5711's used anyway? does their being Shottky diodes make them any
better in this application?
I did wonder if the slightly larger forward resistance of the 1N4148 might
cause a slightly lower VRFDET, but that doesn't seem to be the case.
To add to this saga......after finding the diodes being faulty, I had the
end of the antenna draped over a certificate on the wall to keep it out of
the way. A sudden rain storm went through accompanied by strong winds, and
there was a spark jumping across the ends of BNC fitting on the end of the
antenna as if it had been connected to a cars spark coil. A grounding
switch is now being installed....
I have lost the odd SWR bridge diode in my 40 or so years as an Amateur,
but this is the first time I have actually seen why....
(the antenna is a 80/40/20m set of 1/2 waves arranged as inverted "V's" up
13m in the center,and single coax fed.)
73.....Ron ZL1TW
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