Single-sideband (SSB) was discovered in 1915 by John Renshaw Carson, who was a “transmission theorist for early communications systems.” Soon after, Renshaw filed a U.S. patent application for SSB modulation which was eventually granted in 1923. The original intent of this technique was to “simultaneously transmit multiple telephone calls on a single electrical circuit.”[1] This technology was further experimented with by Bell Labs who eventually developed a method of removing one of the Sidebands of an AM signal, but keeping the other essential modulation elements.
Many of the first SSB experiments occurred during World War I, and those experiments continued into the 1920’s and 1930’s by various entities such as Bell Telephone Laboratories, the U.S. Navy, and various amateur operators. In 1923 the first experimental one-way transatlantic single-sideband transmission was made from Long Island, New York to London, England.”[2]
However, while much experimentation was taking place, as well as advancements in the technology, it wasn’t until after World War II that SSB became practical for use in amateur radio operations.
Fast-forward to today, SSB is used in many communications systems by amateur radio operators as well as commercial use. It is the favored mode for amateur radio communications on the HF band because it uses transmitter power and bandwidth more efficiently.
Single-sideband uses an amplitude modulated format where the carrier and one of the sidebands are removed. The advantage of removing the carrier and a sideband is that it provides greater spectral efficiency without weakening the signal. One of the methods where a single sideband is produced is in the final amplifier stage, or it can be produced at a low power level and linearly amplified.
SSB offers long distance as well as international communications opportunities for HAM radio operators, as these types of signals can propagate over great distances. SSB can be used on both the UHF and VHF bands, and is the main voice mode used for over-the-horizon skip propagation, where radio waves are refracted off an ionized layer in the atmosphere, and then return to Earth.
A question that is often asked is, which sideband should be used for amateur radio operations? In bands above 30-meters which are frequencies higher than 10 MHz, it is common practice to use USB.
On bands below 30-meters, which is anything lower than 10 MHz, LSB is used. However, an exception on the 30-meter, which is allocated for Morse Code (CW) and digital modes (e.g. PSK31 and FT8).
A brief note regarding 60-meters (5.3 MHz), is this is a channelized band, and permitted operation is on a secondary basis. Permitted modes include USB voice, and is available to General, Advanced, and Amateur Extra Class license holders is divided into the five channels below.
For the 40-meter, 80-meter, and 160-meter amateur bands, it is common practice to use LSB. On 20-meters, 17-meters, 15-meters, 12-meters, and 10-meters, USB is used.
Another question often asked is, how did amateur radio operators determine which bands to use USB or LSB on? One widely accepted story comes from an article published in “March of 1956” in QST Magazine by Anthony Vitale.[1] The article was about a Cheap and Easy SSB transmitter build around the VFO in an ARC-5 Command Set transmitter.
The AN/ARC-5 Command Radio Set was a “series of radio receivers, transmitters, and accessories carried abord U.S. Navy aircraft during World War II.”[2] According to an article on Vitale from August 2020, he based his single-sideband homebrew rig using this radio, and what he ended up doing was generating a 9 MHz signal by adding a crystal-controlled oscillator, “mixed with a 5 MHz signal from the VFO, which was then mixed with the audio.”[3]
As a result of this scheme, the “lower sideband result of this mixing lands on 4 MHz, since 9 minus 5 is 4. That puts the LSB in the 80-meter band.” Similarly, 9 plus 5 is 14, placing the USB in the 20-meter band. So, the ARC-5 provided LSB coverage from 4.0 MHz to 3.5 MHz, and USB coverage from 14.0 MHz to 14.5 MHz…and that’s largely how the convention of using USB and LSB on particular bands developed.”[4]
However, there is some doubt about Vitale’s homebrew kit being the genesis of the convention. In an article from August 2021, a counter-argument is made that Vitale may not be the source of this practice because the radio he used had a “phasing SSB generator…and all you would need to do to switch from USB to LSB was a simple switch” which this rig had.[5]
While Vitale may not have been the sole reason for this practice, there were other factors which helped pushed the amateur radio community toward single-sideband. In the 1950’s and 1960’s the “ARRL was behind a big push to get amateurs to switch from AM to SSB” due to overcrowding of the amateur bands.[6] In their efforts to get HAMs to switch, they compiled several articles on the subject which were used to publish a book that featured Vitale’s article from 1956.
Although there are some doubts as to who thought of this practice first, it’s likely a combination of amateur operators like Vitale, the efforts of the ARRL to find a solution to overcrowding of the airwaves, as well as previous design limitations of certain radios.
Current technology has enabled us to switch from LSB to USB with the push of a button. It’s important not to take for granted the experimentation that led to discoveries like single-sideband, all the years of trial and error, and iterations of those experiments performed over decades, all of which culminated in advancing the technology necessary to overcome limitations in communications.
Whether using USB or LSB on a given band was the outcome of a combined synergy, or from a single source, the final result is a method that has become widely adopted and still in use today.
[1] Why the Sideband Convention?: http://n4trb.com/AmateurRadio/Why%20The%20Sideband%20Convention%20-%20formatted.pdf
[2] AN/ARC-5 Command Radio Set: https://en.wikipedia.org/wiki/AN/ARC-5
[3] Why the Sideband Convention?: http://n4trb.com/AmateurRadio/Why%20The%20Sideband%20Convention%20-%20formatted.pdf
[4] Why the Sideband Convention?: http://n4trb.com/AmateurRadio/Why%20The%20Sideband%20Convention%20-%20formatted.pdf
[5] W2EWL’s Cheap and Easy SSB Rig: https://soldersmoke.blogspot.com/2021/08/w2ewls-cheap-and-easy-ssb-rig-and.html
[6] Why the Sideband Convention?: http://n4trb.com/AmateurRadio/Why%20The%20Sideband%20Convention%20-%20formatted.pdf
[1] Wikipedia – John Renshaw Carson: https://en.wikipedia.org/wiki/John_Renshaw_Carson
[2] Amateur Radio and the Rise of SSB: https://www.arrl.org/files/file/Technology/pdf/McElroy.pdf