The link below shows my attempt to build a 3-watt transmitter for 40
meters or 80 meters, based on an article in QST, June 1967 and an
adaptation thereof by KC6WDK.

http://www.kcnet.com/~oyster/transmi...ansmitter.html

I've had some success since I posted last, but I want to get the
output clean before I go on the air with it. I've had very little
spare time, but I've managed to improve the performance quite a bit,
through a lot of frustrating trial and error.

The good news: The transistor does not become egg-frying hot anymore.
Now it's just barely warm. I began trying the suggestions about
grounding and parts placement provided to me by the good people at
rec.radio.amateur.homebrew and qrp-l. What seemed to help the most
were the grounding suggestions; I moved several components' chassis
connections to within an inch of Q2's emitter, and that seemed to help
to increase the output and decrease the self-oscillation, which can
now be eliminated via the variable caps for the oscillator and
amplifier stages (C1 and C2). I also realized how close the crystal
was to Q2 in my original assembly, so I moved the crystal over near
the oscillator section, and that seemed to help, also. The chirp is
still a little bothersome, but the transmitter appears to be putting
out around 2 watts into a dummy load, sans lowpass filter.

I got good results by isolating C2 from the chassis, and grounding it
via a separate wire to the point where Q2's emitter is grounded.

I'm having quite a time trying to get rid of harmonics, which I'm
"measuring" using my Icom R71A receiver, which is across the room from
the transmitter now. Slowly but surely I am making small
modifications resulting in small improvements. I'm rebuilding the
coils now. More details and new pictures of the rebuilt transmitter
are on the website. Thanks to all who offered advice, and any further
advice is more than welcome.


-John Sandin KC0QWE

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