The carrier is not in the middle of the passband of the filter,
otherwise if so, one would have a DSB signal not a SSB signal Thus to
swap sidebands, the BFO frequency must change to the opposite side of
the filter and is placed down the slope some 3 dB to 6 dB.
Carrier frequency + / - the modulated audio frequency produces two
sidebands, one of which is eliminated by the filter.
And if you used a wider filter at least one of your BFO frequencies (and
possible both) would have to be adjusted away from the manufacturers
nominal value in order to maintain the same opposite sideband rejection.
Having done that, the frequency readout for whichever sideband the BFO
had been adjusted for would no longer be correct. Some sort of firmware
modification would have to be done to get it right.
DE N6KB
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