[Elecraft] Elecraft Digest, Vol 263, Issue 15

[Ronald Motyl]

I've also seen the same issue with KX3 in DATA mode, WSJT-X improved, FT8
(w/ Grid Tracker & L4OM, FWIW). Using the AX3 antenna connected with ≈ 10'
RG-8X.

This was using KX3 direct and with the KXPA100.

Would a choke help resolve or reduce this issue?

Is it unusual to see SWR jump / change that much during a transmission?


Ron Motyl
KJ2J


On Sat, Mar 21, 2026, 14:17 Brian Collamer via Elecraft <
elecraft at mailman.qth.net> wrote:

> Hi Tom
>
> My KX3 does the same thing when using Hamlib with WSJTX....
>
> Brian
> KB1OPD
>
> On Sat, Mar 21, 2026 at 12:04 PM <elecraft-request at mailman.qth.net> wrote:
>
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> >    1. K3 high SWR at end of transmission (w2yf)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Fri, 20 Mar 2026 20:01:44 -0400
> > From: w2yf <w2yf.radio at gmail.com>
> > To: elecraft at mailman.qth.net
> > Subject: [Elecraft] K3 high SWR at end of transmission
> > Message-ID:
> >         <CA+_pMJYDgoywTd=-vE=-
> > 41EMnkS9QLnCbPHnYGah1ow6tOPzHA at mail.gmail.com>
> > Content-Type: text/plain; charset="UTF-8"
> >
> > I've run into an interesting issue:
> >
> > I get a high SWR report from the SW; command on a K3 -- only at the end
> of
> > a transmission cycle.
> >
> > Things I have tested:
> >
> > - Occurs on ANT1 or ANT2.
> > - Occurs when LPA is engaged (5w) or PA is engaged (25w).
> > - Always occurs, if transmission is 15 seconds long, or 3 seconds long.
> > - Occurs on antenna matched at 1.3:1 and a perfectly matched dummy load.
> > - Occurs with ATU engaged and without ATU engaged.
> > - Is only at the end of transmission as the transmission envelope is
> > falling off
> > - I have calibrated the transmitter, identical results as above.
> > - All coax has been swapped -- identical results.
> > - SWR throughout entire transmission is 1.1:1, but then when PTT closes
> it
> > reports 20.9:1
> > - Bar graph on K3 shows no SWR variance at all, from the bar graph
> > perspective it is as if nothing is happening with SWR... this only
> appears
> > when polled via the "SW;" command (via Hamlib).
> >
> > Is this a known bug in the K3 firmware? Is it symbolic of hardware that
> is
> > on the edge of failure?
> >
> > The fact that it occurs only at the end of transmission and never during
> > (regardless of length) is odd.
> >
> > Tom, W2YF
> >
> >
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> > End of Elecraft Digest, Vol 263, Issue 15
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