Quadrature techniques for selectable sideband demodulation, akin to the once-popular phasing method for transmitter sideband generation, have been known for many years.
Norgaard (W2KUJ) described a practical design in 1948 (or a little earlier) that was quickly developed as the add-on “Single Sideband Selector” type YRS‑1 (with 14 valves!) converter for communications receivers by the General Electric Company of America.
This allowed selection of individual sidebands, or both (with a locked oscillator this was equivalent to our familiar synchronous AM).
As delivered, the YRS‑1 routed audio back to the receiver AF stages. However “this truly wonderful gimmick” was promptly modified by one employee, George H Floyd: the “Lighthouse Larry” editor of G-E Ham News (an anthology of his SSB-related articles was published as the Sideband Handbook).
That modification delivered sidebands separately and simultaneously to split headphone channels, described as a binaural system in a G‑E Ham News from 1951.
Dinsdale also reviewed an unmodified YRS‑1 in the July 1948 Wireless World but nowhere hints at the possibility of binaural listening.
From the early 1970s onwards Pat Hawker (G3VA), in his Technical Topics column for the RSGB journal Radio Communications (and occasionally in Wireless World), was a frequent commentator on the technology and consistently referred to it as “bi-aural”. Nowhere does he appear to confirm having first-hand experience of such equipment.
Confusingly, the term “binaural” nowadays more usually refers to a completely unrelated sound recording technique, but even this is often called “bi-aural”.
The CCIR Study Group 10 compared various detection methods, rating their “relative effectiveness” in dB for different modes, and the results were tabulated by Haviland (1969, EBU Review) as follows (where we have edited the mode abbreviations slightly and re-ordered the rows):
|DSB+C (10 kHz)||-3.2||–||-6.5||-3.2||-3.2||+2.8|
|DSBC-C (10 kHz)||–||–||+7||+10||+10||+16|
|NBFM (10 kHz)||-20.4||-7.4||-10.4||-7.4||-7.4||-1.4|
|SSB+C (5 kHz)||-3.4||–||-0.4||-0.4||-3.4||-0.4|
|SSB-C (5 kHz)||–||–||+10||+10||+7||+10|
* What can “select product” be?
From these figures, and the favourable comment it has generated at various times during the last seven decades, we dare to hope that SDR technology will bring about a resurgence of interest in binaural.