Right from early 1890s when Guglielmo Marconi first demonstrated that he could successfully send a radio signal from a simple spark gap transmitter to a radio receiver that was only a few paces away, people have been trying to get their radio signals to get out for longer distances and be heard. And as the radios became more powerful and the transmitters more efficient, they could soon send their radio messages (still using Morse code) for maybe a mile or two.
But then the radio engineers and designers quickly discovered that fairly low-frequency radio signals in the MF or HF bands could often travel hundreds of miles, and sometimes thousands of miles. In the very early 1900s, it became possible for two way radio stations to communicate from one side of the Atlantic ocean to another, and for shore-based radio stations to send and receive morse code messages to and from ships at sea.
This meant better safety for the passengers on those ships, and the companies building these two-way radios would lease their equipment – complete with trained radio operators – to handle all the radio traffic from ship to shore, or from ship to ship. Every message was sent as a radio telegram, and was charged for at so many cents per word.
Ships radio operators (telegraphists) who worked the maritime radio bands were often nicknamed Sparks or Sparkie because of the buzzing sparks which sounded from their radio transmitter every time the morse key was pressed closed. Those radio telegraphists could send and receive morse code signals quickly and copy the incoming messages in their heads before writing the words to paper. And they could often hold a conversation with you at the same time!
The early spark gap morse transmitters were large and cumbersome and required vast banks of big heavy lead-acid batteries to power them, and they needed big wire antennas that were hung between antenna towers on land or between the ships masts at sea.
By the end of World War One, the military had discovered two way radio, valves had been invented and the radio sets were a bit smaller and much better quality. By now, they could fit into a horse-drawn wagon. But the early valve radios still used morse code.
Voice signals came during World War Two, but morse code was still used extensively because it could be send and received where the inefficient AM mode voice signals could not be heard. By the end of WWII, the radios were small enough to fit into suitcases and were often used that way by spies and secret agents. And yes, they still used morse code, and they had to string up their wire aerials and send their messages without being caught. By now the military everywhere had security agencies who could trace where the radio signals were coming from and would rush to try and capture the radio operator who was sending them.
These HF (shortwave) radio signals that needed to travel hundreds of miles would only be able to get through at certain times of the day or night. They rely on the radio signal going up into the sky and bouncing off the different layers of the atmosphere so the signals could come back to earth a long distance away. If you picked a bad time of day the atmospheric propagation wouldn’t reflect your signal back to earth, so it couldn’t reach the people you were trying to send it to. But it could be picked up locally where, if you were a spy, you didn’t want anyone local to hear it.
By around 1940, the Motorola corporation created the first-ever walkie talkie radio. It was a clumsy tin box with separate built-in microphone and earpiece. It had tiny valves inside (because transistors had not been invented yet) and pretty heavy battery pack, and it had a telescopic arial or antenna. It could transmit in AM mode (amplitude modulation) and, if you were lucky, it was good for talking over a distance of about half a mile.
That half mile or so distance that simple radios are good for is what we call line-of-sight, and that’s just about the distance you can get today with most cheap walkie talkie portable radios – such as FRS/GMRS radios in the US or the little handheld UHF-CB radios we use here in Australia. Their signals go up into the sky as well, but at those high frequencies (VHF and UHF) they don’t bounce back to earth. It takes a satellite to bounce those radio signals back to the ground, and I (and probably you too) cannot afford them.
73 de David, vk2dmh
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