[Elecraft] K3 high SWR at end of transmission

[w2yf]

Jack,

The KX3 also exhibits this behavior. This is during FT8 transmissions using
Hamlib that these values are given to WSJT-X, which promptly kills the
transmission, if the stop transmit when SWR exceeds 2.5 box is checked...
fortunately the transmission is ending anyway, but you then have to go back
to the system and reenable transmit before continuing on. This is release
4.7.1 due out soon...(currently a release candidate version in the daily
updates)

It is likely the KX2 would also do this (and K3S) although I haven't had a
chance to test.

I'm not expecting firmware re-issued for the entire K-line... but if there
is a solution that the Hamlib guys can program around that works it would
be nice.

K4's do not do this by the way, but they also do not use the antiquated SW;
command.

Tom


On Wed, Mar 25, 2026 at 5:23 PM Jack Brindle <jackbrindle at me.com> wrote:

> I agree with others that because of the way Forward and Reflected power
> are measured by the microcontroller it is susceptible to end of
> transmission glitches, where there is a large drop-off between when the
> forward voltage is converted by the ADC and then the reflected voltage.
> That is probably about 40 to 50 microseconds apart, which is significant
> when power is dropping. I don’t have access to the firmware sources, so I
> can’t tell exactly how the SWR command is handled, nor any side-effects, so
> all we can do is guess. I learned long ago that it is best to not
> second-guess Wayne.
>
> I would suggest that you re-issue the SW; command when you encounter this
> situation, to verify that the issue persists. I doubt if you have to do the
> store than once, but it is possible. If the further readings show no
> problem, then you can safely ignore it. SWR reporting is kind of a
> hit-or-miss thing. In fast-changing modes such as CW or SSB the forward
> power changes rapidly, and the difference between measuring points can show
> up as an error. Of course when transmission stops this is almost certain to
> happen, depending on exactly when the measurement cycle coincides with
> power drop-off. I believe this is what you are seeing. A new SWR request
> should show it. Wayne may not be correlating SWR read with PTT
> de-assertion, so he may not be catching the situation when it occurs. This
> is quite understandable.
>
> At this point in the life cycle of the K3, there won’t be any updates, so
> it is best that you double-check responses when you see anomalies such as
> this.
>
> 73,
> Jack, W6FB
>
>
>
> > On Mar 25, 2026, at 2:38 PM, w2yf via Elecraft <elecraft at mailman.qth.net>
> wrote:
> >
> > Jack,
> >
> > I am using all the  latest firmware versions for all subsystems of the
> K3.
> > As I mentioned you only see this if you are using SW;.
> >
> > I've never seen the bar graph indicate any change in SWR which is why I
> > think it is a bug. If it was a true measurement I would think the
> firmware
> > would jump the bar graph or throw a "Hi SWR" on the display.
> >
> > 73s,
> > Tom, w2yf
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