Telephone carriers deserve the credit for most of the early development. They are the real long distance SSB pioneers.
Radio was first used for long distance phone calls in 1927. Signals were carried over massive long-wave stations on either side of Atlantic Ocean, on a frequency of 60 kHz. Over the next two years, long distance phone coverage expanded onto short-waves, as well.
Because of the huge investments in the radio systems, as well as the need for human support along the way, long distance calling was initially quite expensive. Calls were limited to 12 minutes. The charge was an equivalent of $350 per minute, in 2017 dollars, between London and New York.
According to The Worldwide History of Telecommunications: “Whereas two operators in London and two in New York could handle the calls, a total of about 40 persons were required to operate the four long-wave and the two
shortwave stations. In the first year an average of only seven calls per day were established, originating almost equally in the United States and in the U.K., but this increased to about 50 in 1929.”
Within another five years, similar systems had sprung up around the globe. Prices dropped by 70%, but were still costly at $125 per minute.
Early Long Distance SSB Telephone Technology
Engineers at Bell and other phone companies initially selected long-wave frequencies as best for distance voice communication. They also leveraged their ten years of experience in using single-sideband for sending voice circuits over cables. Stations were located in remote areas, mainly to get away from interference given off by automobile ignition systems. Long-wave offered 80% reliability over the Atlantic routes.
Typical transmitter power was 50 kilo-watts. The favorite receiving antenna was the “travelling wave” wire, later called the Beverage. These were typically at least one wavelength long – often 4 to 5 kilometers of wire mounted 8 meters above ground. Very directional and low noise – still used by listeners on lower frequencies today.
Audio was limited to a band of 400 to 2600 Hz, the intelligence bearing frequencies. In order to get good quality audio from long distance SSB, frequency accuracy of 0.017% was needed and achieved.
All of this happened 30 years before hams started using single-sideband suppressed carrier for amateur radio.