[Elecraft] K3 high SWR at end of transmission

[Bob McGraw]

I just checked my K3S, ATU bypassed, on 3 different bands, 2 different 
antennas.   Frequencies were chosen such that  SWR values were 1.1:1, 
1.5:1, 2:1, and 4:1.   This issue was not observed via the K3S SWR display.

I would be inclined to look at the spectral output using a spectrum 
analyzer in the event something is breaking into oscillation.    Also 
try it on a 50 ohm dummy load.   It it isn't seen there, then something 
is breaking into oscillation on PTT drop out.    A 50 ohm dummy load 
will be 50 ohms at all frequencies where as the SWR will only be low at 
the antenna matched frequency.

73

Bob, K4TAX

On 3/23/2026 11:00 AM, elecraft-request at mailman.qth.net wrote:
> Message: 3
> Date: Sun, 22 Mar 2026 21:16:50 -0400
> From: w2yf<w2yf.radio at gmail.com>
> To:elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 high SWR at end of transmission
> Message-ID:
> 	<CA+_pMJZXt6kLYC8+L3kV8OP3ywWw5rRS6ayDqisakTywYaAD3Q at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Bob,
>
> I was hoping PTT-RLS would do the trick, as I was reading the description
> it sounded like it would solve the problem. Unfortunately, tweaking this
> parameter didn't fix it.
>
> I tested my KX3, different radio, different computer, different
> everything... it does the exact same thing... so maybe the whole K-Line
> does this.
>
> It is problematic when you have software releases of WSJT-X that have a
> feature to auto-shutoff transmit when SWR exceeds 2.5, but of course it
> shuts off every iteration since it appears the radio is giving incorrect
> SWR values at close of transmission.
>
> I thought this would be a great feature, especially when mobile and antenna
> SWR can get a little edgy, but if the transmitter doesn't give correct SWR
> values, that feature isn't useful.
>
>
> Brian,
>
> Thanks for the extra data point... so I'm not the only one.
>
> Tom, W2YF