Re: K3 Power Reading/SWR/ALC Problem

Posted by Bob McGraw - K4TAX on Jan 21, 2018; 10:14pm
URL: http://elecraft.85.s1.nabble.com/K3-Power-Reading-SWR-ALC-Problem-tp7637545p7637562.html

 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>
>
>
>
>
> --
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