From experience, I'd say nearby lightning strikes would be the
culprit. I strongly urge everyone to use protection devices on all
coax and balanced lines at the point where the feed lines and rotor
lines enter the house. I prefer Polyphaser devices. Don't buy cheap
or ham fest bargain table crap! Your radio and your house depends on it.
I don't disconnect antennas nor do I ground antennas. I protect for
lightning outside and prefer to choose methods where it will not be
allowed in the house. And I'm on a hill and have two towers which
are 500 ft above average terrain out to some 35 miles. I understand
lightning and what it can do. As to lightning, mitigation is the
approach, elimination is not physically possible.
73
Bob, K4TAX
On 1/21/2018 3:42 PM, ab2tc wrote:
Hi Don and all,
I really don't understand why static build up on the antenna should be a
problem with the K3. Due to the (good) design of the SWR bridge (a two
transformer design with a voltage transformer right across the output) the
antenna port presents a dead short circuit at DC both in receive and
transmit. I just verified this with an ohm-meter (in receive only - no need
to check in transmit since the SWR bridge is surely present then - don't
want to kill my DMM).
Maybe we are talking semantics here but it appears to me that the cause of
diode damage in the SWR bridge circuit is more likely caused by transients
induced into the antenna system by nearby lightning strikes than static
buildup.
Knut - AB2TC
Don Wilhelm wrote
Paul,
The diodes are the most likely suspect, so replace them first and
re-check.
You are correct that the problem is that the wattmeter is not feeding
the power back to the MCU and the power becomes uncontrolled.
Wattmeter damage is normally a result of static coming in on the antenna
feedline. If you do not have an means of disconnecting the antenna when
not in use, it would be wise to add that - switching the K3 to a dummy
load would be a good addition too.
73,
Don W3FPR
<snip>
--
Sent from: http://elecraft.365791.n2.nabble.com/
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