What The Tech?! Single Sideband Transmitters

Single-sideband transmitters (SSB) enabled mobile stations to use radio reliably over longer distances.

As we’ve explored communication through our What The Tech pieces, we’ve looked at different ways and evolutions we used to communicate. There’s the telegraph, the radio transmitter and satellite linking that all played a part in bringing together our connected world. However, before mobile phones when radio was king, there was a certain type of radio that made communication over long distances far more reliable. Yet, in today’s world, it’s relegated to the history books for many people. But when satellite coverage is dark and there’s not a mobile phone tower in sight, this mode of communication is often still king greater. Today, we’ll be looking at the role single sideband transmitters played in connecting our world.

Radios: Modulation and Mechanics.

 
While the radio transmitter is no stranger to our columns for the impact it had on our world, the fact is that like people radios come in an assortment of different shapes, types and roles.
 There is an assortment of modulation types and modes. We explore some of these in depth in our Radio Hackers publication. Source: Wikipedia
While most people are familiar with the AM/FM receivers that are fitted in vehicles, there’s an assortment of what we’d call Modulation Types, that all have different benefits, downfalls and other factors that influence their use case. For instance. FM (Frequency Modulation) radio, like what you’ll often listen to in a vehicle suffers from a phenomenon known as the Capture Effect”. Without wasting time on a physics lesson, what this effectively means is that when two signals collide, the strongest signal wins the day, drowning out the other entirely.
So if we were to use FM in say, an aviation environment then should two planes transmit at the same time as you’d imagine, having one transmission drowned out is pretty poor for contributing to situational awareness and increases the chances of an accident substantially. Instead, for aviation we use AM (Amplitude Modulation), and when two transmissions collide while often neither of them is legible, this collision is easy for Air Traffic Controllers to hear and detect.
  Modulation Types. Base, AM, LSB USB. Source: Wiki
When we’re looking at the attached image, we can see that the AM signal contains three parts. The middle carrier wave, and two sidebands, which are known as the Upper Sideband and the Lower Sideband. When we are using an SSB transmitter, the middle carrier wave and one of the sidebands are suppressed. This leads to a lower signal bandwidth, greater power output and more reliability, although like anything, there are some downsides.
Typically, SSB transmissions are sometimes noisy, susceptible to both weather and man-made interference and will often require a bit of operator skill to get the best out of the systems as well as a reasonably good antenna. However depending on your power output, antenna selection and band choice, you’ll find that in a lot of circumstances, SSB communications can be carried out pretty reliably over long distances.
  Early transmitters used Vacuum Tubes before moving to solid-state circuitry with the evolution of electronics. Source: Wikipedia

How Did It Start

 
Like many evolutions with communications, the first discovery of SSB occurred in 1915 with experiments relating to WW1. While the usage was small-scale, commercial services took off a decade later in the mid-1920s and by that time WW2 came around the SSB transmitter was becoming a more familiar site in both ships and aircraft.
In fact, SSB was so important to the Allied war effort that one of the methods of encryption during the war used SSB transmissions processed in a certain way to provide a semi “secure” service. Known as SIGSALY this system was responsible for many firsts however due to its functioning on the basis of voice-based encryption, cryptographic advances meant that it didn’t take long to become obsolete.
  SIGSALY was advanced for the time, providing secure communications. The downside was it took over fifty pieces of rack-based equipment to run! Tube gear could be pretty crazy. Source: Wikipedia
With WW2 providing a general boost to communications research and techniques, by the time the war came to a close, the mode had attracted the attention of Amateur Radio operators. Many of these hams had military service experience and brought this experience to their hobby, with amateur radio having its boom time in the post-war peaks before household telephones really became a proper thing.
By the time the 50s came by and the Cold War was in full swing, SSB was the defacto method of communication for Strategic Air Commands bomber fleet, and due to large investments by the military, usage of the entire radio spectrum including single sideband became more common, more efficient and more easily understood.
  SSB was an essential part of the Strategic Air Command’s communications strategy during the Cold War. Source: Wikipedia

Civilian Usage

 
If you weren’t part of the radio craze that took hold in the 70’s and 80’s you’d be forgiven for thinking that this was relevant to only the military or in some instances, commercial applications. However, the evolution of SSB was kind of like the gyroscope in that it was relevant to everyday humans far more than they realised even if they didn’t know it!
For instance, in the days before mobile phones, SSB was a transmission mode that was used for long-distance telecommunications. In the early days, this was voice only but as the technology evolved digital techniques evolved with it and computers and the internet started to take hold. The world of amateur radio didn’t sit still either and Amateur (Ham) operators used SSB as the foundation for discovering and experimenting with new communication modes as well.
We’ve always made the point that in life, it’s often good to have a back communications strategy as sometimes things just happen. So now it’s story time as we look at a moment when SSB and Radio saved the day.
  Cyclone Tracy as it approached land. Source: Wikipedia.
70’s Australia was apparently, a simpler time. Television was still a relative novelty, many of the continent’s roads remained unpaved and cities like Darwin stuck out as beacons of life in a hot, red dust environment that was remote, and far away from what many classed as civilisation. Jet Aviation was still building in the post-war era and while the telephone was around it wasn’t established in every house like some of the older folk might remember as it was at its peak.
On Christmas Eve 1974, terror struck Darwin as Cyclone Tracy made for land. The storm, which would eventually rage for the night reached peaks of over 217km/h before instruments failed and would by the end, be responsible for destroying most of Darwin, causing 857 million dollars in damage and taking over 70 lives in the process.
As the sun rose on Christmas Day, Darwin lay in debris, a naval ship was destroyed and over 31 aircraft lay in ruins at Darwin airport. The worst bit though? The storm had destroyed basically every military and commercial telephone or radio system in the entire town. Darwin was alone, and mute, right when she needed to speak.
  Darwin, Christmas Day 1974. Source: Wikipedia
Thankfully, two things came into play. A wiley amateur radio operator, Bob Hooper (VK8RR) was able to get a station assembled and at the same time, people assessing damage at the airport were able to remove a working HF radio from an aircraft that survived the storm which was later used to set up a secondary station. These stations, which would later be joined by a maritime station passed large amounts of emergency traffic and gave Darwin a connection to the outside world when it needed it most. It’s pretty fair to say that in most natural disasters having an alternate way to get a message out is never a bad thing.

Legacy on the World

 
While inventions like the mobile phone, and GPS are easy to recognise in terms of their importance in everyday life, it’s fair to say that the SSB transmitter has escaped recognition for the importance it had in the growing, technology-based world.
While in today’s world, we’re more likely to use a satellite phone over a single sideband or HF transmitter, the fact is that these transmitters still play a role in the modern world, albeit a smaller one.
Airlines use SSB on HF for intercontinental travel, giving a way for aircraft to safely communicate thousands of miles away over the open ocean.
  HF Capable systems are still on long range aircraft. Source: Quora
Maritime stations will still carry an HF transmitter and while often, a satellite phone has replaced them you’ll still find a backup transmitter on the bridge ready to get to work should that link fail.
And in remote areas like the Canadian & Australian wilderness, both Police and Military still find use for the SSB HF radio even today, using it to find a link when little else works. CODAN, an Australian manufacturer of HF transmitters and receivers can be found on each continent of the world at this point, and systems like the Automatic Link Establishment setup make opening and maintaining a relay link a far easier task using modern technology.
  A modern, CODAN HF SSB radio. Source: codan.com
While mobile phones and the internet are definitely cool, there’s still something intriguing about using a wire a battery and a transmitter to send a message hundreds or even thousands of miles.
What the Tech?! is our recurring, twice-monthly piece on the the technology that helped shape our modern connected world.
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