Don, as described that was NOT the opposite sideband. On the video the
stronger signal was at 14091.883 kHz on the dial. That is the frequency
of the mark tone; the space tone would have been at 14091.713 kHz. The
pitch in use was 915 Hz mark, so the suppressed carrier frequency would
be 14092.798 kHz and the center of the filter bandpass (the notch in the
dual passband filter pattern) would be at 14091.798 kHz (1000 Hz below
the suppressed carrier).
The second slightly weaker signal in the video was at 14091.720 kHz,
i.e. the higher of its two tones was virtually coincident with the lower
of the two tones from the first signal, and the second tone would be 170
Hz lower, at 14091.650 kHz.
A true opposite sideband signal response would have been at
14093.713/14093.883 kHz, nowhere near what was observed.
This resembles audio IMD more than an opposite sideband response. For
example, a heavily overdriven audio signal with two overlapping
simultaneous tones at 915 Hz and 1085 Hz might develop spurs at 745 Hz
and/or 1255 Hz, and one of those spurs combined with one of the intended
tones in the first signal would look a lot like the second signal in the
video.
My next question would be, do you see something similar if the dual
passband filter option is turned off, or only when it is turned on? I am
wondering whether some kind of aliasing phenomenon could exist in the
dual passband filter that might account for this.
73,
Rich VE3KI
W3FPR wrote:
For strong signals the filtering may let some of the opposite sideband
get through the filters.
What is the relative S-meter reading for the true sideband and the
opposite sideband?
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