Synthesis and Analysis of a Single Side Band signal.

by VA7KL ex-VA7FFT

A few methods of Single Side Band generation and detection are well-known to the ham radio community, namely: filtering, phasing and Weaver methods [1]. They all perform "Analysis" of modulated RF carrier on RX and TX: suppression of unnecessary sideband, and selection of required sideband. "Analysis" of SSB signal, nowadays, is mainly performed by quadrature detectors, to obtain I and Q channels for subsequent SDR processing. Such detectors require strict balancing by amplitude and phase.

"Synthesis" of SSB signal, on the other hand, is less known and less used. Even the modern direct-sampling SDRs, DUC/DDC use the Weaver method. Today it is impossible to find out who first recognized that the phase of SSB signal is equal to the speech phase, and that the SSB envelope is the same as speech envelope. So if someone measures those two speech parameters in real time, and uses them to generate an RF carrier - it will have only one sideband. Today SSB synthesis is used only in the minimalistic QRP transceivers [3,4], with rather simple hardware: 8-bit ATMEGA328P and SI5351A (which is amazing). It would be interesting to investigate Synth-SSB possibilities, not being restricted by hardware resources. For that (and for other projects) I have built a few Development boards on a dual-core STM32H747 controller and four-channel AD9959 DDS. After bare metal programming of the hardware and the Hilbert transform [2], finally I am on the air !

My first QSO with Synth-SSB on TX was with WB7NZI and KC7KIU on 3,998 kHz at 9:35 PM PDT July 28 2021. SSB RX was with the conventional quadrature detector by phasing method. Excited by success, I developed the serial quadrature detector for RX.
My first QSO with both: serial quadrature detector on RX and Synth-SSB on TX was with BCPSNet on 3,729 kHz at 5:30 PM PST January 25 2023 - pls compare the recordings below.


The first QSO with both: serial quadrature detector and Synth-SSB is with British Columbia Public Service Net (BCPSN), streamed to Youtube 2023-01-25, net side and my side (70wt linear PA):


The latest QSO with Synth-SSB only is with British Columbia Public Service Net (BCPSN), streamed to Youtube 2021-12-29, net side and my side (70wt linear PA). This is the latest embedded software, no filtering or other tricks, but with all defects fixed. Previous audio artefacts are gone:


BCPS Net was streaming to Youtube 2021-08-04, net side and my side (70wt linear PA). Compare the audio and panorama of my VA7KL with VA7QB (ICom7300 100wt) and VE7CRT (KX3+KXPA100 100wt), from nearby QTH:


BCPS Net was streaming to Youtube 2021-08-11, net side and my side. Compare my VA7KL with VA7QB and VE7BCJ from nearby QTH:



Development board (for sale, I have a few of them):



Control & Indicators board, static, I2C driven:




References:

[1] https://en.wikipedia.org/wiki/Single-sideband_modulation

[2] https://en.wikipedia.org/wiki/Hilbert_transform

[3] http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll.html

[4] https://groups.io/g/ucx

© 2023

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