Steve:
Is it possible your dummy load is not 50 ohms at 6M? In other words, is
your dummy load designed to work at VHF frequencies? Maybe it's only
designed for HF frequencies. Just a thought, but it could possibly
explain your problem.
73,
John AA0VE
Jim Rodenkirch wrote
I'm not sure I understand......are you saying with the ATU removed the
VSWR is 1.2:1 and with it
installed but not tuned it's 1.8:1 until the ATU "kicks in and does its
job???
Hi Jim,
Sorry for the confusion. I'll pull everything into this post to put it in
the correct context:
Problem:
6M band -> VSWR 1.8:1 (KX3 meter) on 50ohm load connected directly to ant
connector (no cable).
ATU - bypass mode
Load verified good.
All other bands good.
ATU will match to 1:1 if enabled and tune requested.
After ATU match, 25ohm load yields 2:1 (KX3 VSWR meter test - OK).
So the issue was that the ATU in bypass mode on 6M into good load gives a
1.8:1 VSWR.
Working with Elecraft support, I removed the ATU board to check VSWR w/o the
ATU in the line. That checked good 1.2:1. The ATU in bypass mode on 6M does
not quite function as a 50 ohm transmission line. For my particular unit,
it was higher than expected. 1.4:1 is considered OK. If the ATU is enabled
and tune is engaged, it has no problem matching the output stage to the load
and delivering rated power. So, operationally not really an issue. Just
leave the ATU enabled and tuned.
The reason for going into bypass mode was to perform a TX gain cal
procedure, which specifies the ATU must be set to bypass. I used the KX3
utility to do this and it sets the ATU to bypass and steps thru each band.
When it got to 6M, it failed - probably because the foldback circuit was
kicking in @ 1.8:1 and/or the output stage can't deliver the 6 watts need to
complete the cal into that mismatch. Doing the cal manually with the ATU on
and matched for 6M band works fine.
Hopefully, this provides a more useful note for anyone else that may have a
similar issue.
Trying to contribute back to the list - as I have learned a lot using this
resource.
Steve
WD4SDC
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