[Elecraft] K3 Power Reading/SWR/ALC Problem

[Dauer, Edward]

I missed the original post that began this thread, so the following may or may not be relevant.  I gather the question is about voltage spikes on the antenna or feedline that damaged something nearer the transmitter end.  If that is so, I would ask the original submitter if they are using a remote antenna switch that couples the relay DC through the feedline.  If so, you might examine the switch to see if the proper diode protections are present on the remote relays.  Some time ago I had the PA transistors in a new K2 blown away three times, until Don Wilhelm put me onto an investigation in which I saw on a scope very high voltage short-time-rise spikes on the line when the relay coil fields collapsed, from an MFJ remote switch system that was sold before MFJ changed its design to include those protections.  Just a thought from a bad experience.

Ted. KN1CBR

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    Message: 6
    Date: Sun, 21 Jan 2018 16:14:55 -0600
    From: Bob McGraw K4TAX <rmcgraw at blomand.net>
    To: elecraft at mailman.qth.net
    Subject: Re: [Elecraft] K3 Power Reading/SWR/ALC Problem
    Message-ID: <9ff00d5b-d3ba-c49c-0293-c5d93e34696b at blomand.net>
    Content-Type: text/plain; charset=utf-8; format=flowed
    
     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
    >
    >