"I haven't worked any AM yet with my O II, but I've listened a fair bit.
I've not heard any of the distortion spoken of so far. But I'm certain
that the 6 kHz bandwidth limit imposed by th eroofing filter severely
affects the audio quality. There are no frequency components above 3 kHz
hen using AM. Yet, if I listen to the same signal in SSB with the BW set
to 6 kHz, AM sounds better than I've ever heard it."
This makes perfect sense if the 6 kHz 1st IF filter is selected for both AM
and SSB modes. In AM, the LO carrier set point is placed in the center of
the filter's passband, leaving 3 kHz on each side for simultaneous USB and
LSB detection. In SSB, the carrier set point should be placed at either end
of the lower or upper skirt of the 6 kHz filter, depending on USB or LSB
modes, leaving detection of a full 6 kHz of available passband.
Accordingly, an AM station detected in either SSB mode with the 6 kHz
roofing filter should produce 6 kHz of audio passband.
Not owning an O2, I am just guessing as to how the 6 kHz roofing filter
should operate based on the feedback I'm seeing here. Can anyone confirm?
Paul, W9AC
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