[Elecraft] K3 TX power foldback with SWR

[Dave New, N8SBE]

Mike,

I've encountered this on my K3 and K3s in the past, and one thing is 
that the output power will recover after several seconds of 
transmission.  I complained about this, and someone on the list pointed 
out that temporarily doing 'something' (sorry I don't remember what now, 
since I haven't touched my K3s since I upgraded to a K4D) would 
immediately clear the issue.

Seems I remember that rebooting the K3 would do it, but that's a rather 
drastic measure to take in the middle of a contest, especially because 
some logging programs will complain quickly if the radio port is missing 
for even a couple of seconds.

Not sure what search terms to use to find that conversation.  Sorry I 
can't be more helpful.  I feel your pain.  I have archives of this 
maillist going back to 2009 on another computer, here.  If I can 
remember, I'll see if I can find the conversation.

73,

-- Dave, N8SBE, Hamshack Hotline 550-0971, HamsOverIP 101018, 
AmateurWire 1348


On 2025-03-03 09:10, Michael Carter via Elecraft wrote:
> For the first time that I can recall, I experienced my K3/100 reducing 
> its TX output power abruptly (from 95 watts down to maybe 5 watts) on 
> first transmission on a new frequency close to the one where the 
> internal KAT3 ATU was tuned.  This occurred on multiple bands in this 
> past weekend's ARRL DX SSB contest.  Since I rarely operate on SSB, and 
> have never experienced this behavior on CW in years of contesting, I 
> was perplexed.
> 
> This morning,  I explored the archive on both the original Elecraft 
> reflector and the Elecraft-K3 at groups.io forum, and I found several 
> mentions of the power foldback behavior.  VE3KI in one old post pointed 
> out that the SWR change due to tuning away from the ATU tuning 
> frequency may be modest, but the change in PA current or voltage may 
> trigger the output power foldback.  I understand the basis for that 
> protection.
> 
> My question:  how does one reset the TX power to full output after such 
> a foldback event?  I tried an ATU retune on the same frequency on which 
> the foldback had just occurred, but that didn't seem to restore full 
> power.  I tried rotating the POWER control knob up and down around the 
> desired output level, and that did seem to reset the TX output power to 
> its original setpoint.  I was just tinkering during the contest and 
> feeling like I didn't fully understand a methodical way to restore full 
> power output.  Guidance from those who have dealt with this issue long 
> ago is most welcome!
> 
> Thanks, and 73,
> Mike, K8CN
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