You are using the matchbox to convert the balanced line to unbalanced
and then using the internal ATU to resolve a match.
Use the matchbox connected direct to your radio, bypass the internal
ATU, and tune the matchbox as needed. That will work great.
If you insist on using the radio internal ATU, get a proper balun to
feed the balanced line, remove the matchbox, and be done with it. That
will also work great.
73
Bob, K4TAX
On 3/10/2025 11:00 AM, elecraft-requ...@mailman.qth.net wrote:
Message: 2
Date: Sun, 9 Mar 2025 17:52:52 +0000
From: Michael Carter<mike.car...@unh.edu>
To: Elecraft Reflector Reflector<Elecraft@mailman.qth.net>
Subject: Re: [Elecraft] K3 TX power foldback with SWR
Message-ID:
<bl3p223mb03855e806499171cb94bf013e4...@bl3p223mb0385.namp223.prod.outlook.com>
Content-Type: text/plain; charset="iso-8859-1"
Hi Jim,
Thanks for your observation. I think that duplicates what I found by fooling
around during the SSB weekend. I tried retuning the ATU, of course, after the
'Hi SWR' message flashed, but that didn't restore full power. I don't have CW
in SSB enabled (because I so rarely operate SSB), but I do think I switched
modes to CW and hit the key, then back to SSB. That might have done the trick,
but I wasn't taking notes : ) .
I just verified that by tuning my Matchbox for lowest SWR (using an AA-55
impedance analyzer) at the midpoint of each U.S. phone segment (40, 20, 15, and
10 meter segments - no WARCs), the SWR is always less than 3.0 across the
entire segment, and for a couple bands it is less than 2.0 across the band,
without further adjustment of the Matchbox controls. That SWR would seem to be
well within the capability of the internal KAT3 ATU. While I didn't train the
KAT3 by first moving up the band in 20 kHz increments and re-tuning the ATU, it
is still surprising that a 2.0 SWR would cause the 'HI SWR' warning and TX
power foldback. I will look at the actual R+ JX impedance values for a better
picture than SWR alone can provide.
73,
Mike, K8CN
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