Single-sideband jubilees

Pieter-Tjerk de Boer, PA3FWM pa3fwm@amsat.org

(This is an adapted version of part of an article I wrote for the Dutch amateur radio magazine Electron, April 2017.)

The year 1915, now just over a hundred years ago, is seen as the beginning of single-sideband technology. A few scientists had already realised earlier that in theory other frequencies arise with amplitude modulation, but in 1915 it was realised for the first time that one in fact needs to transmit only one sideband. H.D. Arnold proposed to tune the (on such frequencies rather narrow-band) antenna of a longwave transmitter of the American navy a bit to the side of the carrier frequency, so that one sideband would be transmitted much more strongly than the other. John R. Carson realised that one could omit the carrier entirely, and got a patent for this. In the following years, single sideband was mostly used on cable connections, to transport multiple telephone calls on a single cable, by converting them to different frequency ranges.

Radio application started in 1922, with an experimental one-way transatlantic voice transmission from the US to England on 57 kHz. After this had been shown to work, a two-way system was built, still at 50 to 60 kHz, which enabled transatlantic telephone calls in 1927, now ninety years ago. (Sea cables at that time did not yet have amplifiers and were therefore limited to telegraphy, and satellites of course did not yet exist.) The first transatlantic telephone call has been recorded and preserved [3].

SSB application on shortwave had to wait for technology to improve further; in the course of the 1930s this started. But also after that, it didn't go fast. In December 1956 (now sixty years ago), a special issue of the scientific journal "Proceedings of the IRE" appeared, dedicated entirely to single-sideband technology, because by that time it was perceived urgent to start using the shortwave spectrum more efficiently. In this issue we find among others Donald K. Weaver's famous article in which he describes the "third" method of generating SSB signals. Another article in this issue is by John P. Costas, in which he favours the use of double sideband, an exception among all the other articles on single-sideband. This article has mostly become famous because he proposed a DSB demodulator which is now known as the "Costas loop" and is at the heart of demodulators for many modern digital radio signals.

In this special issue we also find [5] about the state of radio amateur use of SSB. This article reports that already several thousand amateur stations are working in SSB, "despite the fact that the use of SSB imposes, for the average amateur, comparatively severe technical requirements". Indeed, already eight years earlier, in 1948, articles appeared in QST explaining and popularising SSB (then called S.S.S.C., Single-Sideband Suppressed Carrier) [4]. In the Netherlands, this took a little longer. In the regional sections news of Electron (the Dutch counterpart to QST, RadCom, etc.) of July 1949, we read about a lecture given by OM Prangsma, PA0WP, about it in the Eindhoven section: "although this topic is very popular in America, this turned out to not really be the case in Eindhoven". But this didn't last long; in 1950 a series of articles about SSSC appeared in Electron, written by the The Hague section and OM Van Prooijen, PA0PVP.

SSB with full break-in?

[5] also mentions a surprising advantage of SSB specifically in radio amateur use: "It has also provided a more natural means of communication, since with voice-controlled transmitters and receivers, which are in universal use, it is possible to have "back-and-forth" communication similar to conversation over an ordinary wire telephone circuit." Technically this difference makes sense: with AM, one explicitly switches the carrier on and off, while with SSB there is no difference between transmitter off, or transmitter on but transmitting silence. Some more details are given, see the picture. I find this surprisingly advanced: a VOX, with loudspeaker reception, and switching so quickly that one can interrupt the other; as far as I know this is not standard even now, but was apparently commonplace back then?

References:

[1] Alois Krischke, DJ0TR: 100 Jahre SSB. Funkamateur 3/2016.
[2] Arthur A. Oswald: Early History of Single-Sideband Transmission. Proc. IRE, 1956. (online at IEEE)
[3] http://www.history.com/speeches/first-transatlantic-telephone-call
[4] Gil McElroy, VE3PKD: Amateur Radio and the Rise of SSB. QST 1/2003. http://www.arrl.org/files/file/Technology/pdf/McElroy.pdf
[5] George Grammer, W1DF: Single Sideband in the Amateur Service. Proc. IRE, 1956. (online at IEEE)