Solved the USB/LSB switching problem in my SX-117. As I guessed, the BFO
was out of alignment but not a heck of a lot and I needed to get it back to
its center frequency of 50 khz.
The manual states the BFO frequency is set at exactly (their words) 50 khz.
Looking at the schematic, I determined I could connect my 756pro test rig
through a coupling cap and find out where the BFO was on the spectrum scope.
I found it at 48.6 khz. I unlocked the BFO control, and carefully rotated
the slug till I had exactly a 50khz blip on the scope.
At that point I locked down the BFO (mechanically) and tried the receiver
again. It now acts like a true SSB receiver in that I can no longer receive
USB and LSB in any mode SSB position. USB is now USB and LSB is now LSB on
the mode switch.
One thing is puzzling to me however. The manual says to "not use the BFO to
tune in signals", and "it is set at the factory at exactly 50 khz". Why
then oh why, would Hallicrafters bring the BFO frequency control out the
front panel so you can change the frequency?
Other rigs let you adjust the BFO level or just turn it on or off but they
don't provide a control to change the BFO frequency. My SX-111 just has an
on/off BFO switch. My SX-17 has a BFO level control. Most rigs just have
BFO on or off.
Why Hallicrafters brought out the control, I cannot answer but, I think
maybe this BFO control, the ability to change frequency, was a precursor to
the "IF Shift" control found on many of today's rigs. What do you think?
K2WH
Bill (Group Owner)