>What can REALLY be vexing, though, is when the crystal(s) used in >carrier-generating oscillator frequencies "migrate": I once had an SB-102 >transceiver that sounded very tinny & nasal-sounding on LSB only---much to my >chagrin, THAT carrier generating crystal had shifted just enough so as to put >a goodly portion of my signal REMOVED from the passband of the IF filter!"
Same issue I have with my Collins 75S-3C. LSB audio in the fixed BFO position does not have the same audio passband characteristics as USB. Even small changes (e.g., 50 Hz) can have a profound effect on the tone of the recovered audio. Unlike the R-4C where its two BFO crystals operate at 10x that of a 455 kHz BFO, the 75S-3 has no variable compensating caps to adjust the crystals' operating frequency. However, when switched to variable BFO mode, all is well and the audio tone can be adjusted with the BFO control. INRAD sells replacement BFO crystals for the 75S-3, so I'll likely try those and see if that improves the fixed BFO audio. Paul, W9AC
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