[Elecraft] K3 - AFSK anamoly? No replies, try again

[Richard Ferch]

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?