Following Eric's directions to measure current draw, I realized that I
had low output on all high bands, not just 10/12m.
Using the TX signal tracing procedure in the manual, I isolated the
problem to the TX mixer buffer amplifier, and found it.
Now I have plenty of output on all bands.
Thanks for all the help Eric and Mychael, and for the great
troubleshooting in the manual!
Details for the record:
U9, the TX mixer output buffer, showed approximately unity gain on all
bands.
I wicked and redid the solder joints of U9, to no avail, so I decided to
check the buffer circuit components.
Sure enough, I had neglected to install C150 on the bottom of the board.
I even found the 330pF capacitor in my bag of "parts left over," hi hi.
C150 provides the RF coupling to ground for voltage divider in the
feedback loop, thus setting the minus input of the op amp roughly equal
to its output, making it roughly unity RF gain instead of 11:1. I guess
below the middle of 20M or so, the mixer output itself was enough to
drive the output stages.
73,
Leigh.
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