Re: QCX-SSB: SSB with your QCX transceiver


Kārlis Goba
 

Guido, I was so intrigued by this method of SSB modulation that I made a script to simulate the modulation. Of course, it is an idealisation of real-world components and their speed/linearity, but it gives at least the upper bound of quality for such method. Unfortunately I found that the phase signal exhibits very rapid discontinuities, and as such has a very high bandwidth. Limiting this bandwidth (e.g. by a finite update rate of Si5351 VFO) produces the same kind of artifacts that can be heard in your recording. I found that even 2-3 times the SSB bandwidth could still be insufficient. The envelope signal is somewhat more tame but I guess the quality still suffers a bit from the low-bit quantization in QCX hardware.

I still find the idea of generating an SSB signal by means of class C/D amplifier(s) intriguing. Perhaps using 2 such amplifiers, splitting the signal into I/Q components, and combining it with a lumped element 90 degree hybrid? The PhD thesis I linked here earlier to had some ideas.

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Karlis YL3JG

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