I've gone nuts trying to figure out why I have low output at higher
frequencies. I'm out of ideas and would appreciate any help. I sent a mail
message in a coulpe of days ago about my problems and got some suggestions
on where to start. Many thanks to those who responded. I'm out of ideas so
I'm asking once again for help.
Briefly, power output starts to drop off at 15 meters where I can only get
about 9W out. By the top of the 10M band, I can only get out a few tenths
of a watt. I bypassed the low-pass fiters by pulling the 160M module and
attaching the load to pin 1 of J14. I get the same behavior. This proves
that the problem is up-stream of the low-pass filters.
I visually checked most of the parts related to the transmitter section. I
checked for a stuck relay using my scope. I rewound RFC3, T2, and T3. I was
careful to mount T3 off the card. I've played with alignment with no
success.
I noticed that the output of U10, the Xmit Mixer looks distorted and weak at
higher frequencies, but I'm not sure exactly what the signal should look
like. At frequencies below 15mhz, the mixer input is 4.9137mhz higher than
the tuned frequncy. At frequencies above this, it is the same amount lower.
I assume that the mixer is mixing in the 4.9mhz signal, generating the sum
and difference. The band-pass filter should then pick off one of the two.
I can't really trace the 10m signal through the filters because the
scope-probe capacitance is relatively high compared with the 1pf cap in the
10m band-pass filter.
I could box the thing up and send it into elecraft for them to look at, but
I'd like to fix this myself. Any suggestions and help is appreciated.
Thanks in advance
Rich - KE1EV
http://www.richardcarter.net/_______________________________________________
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