I see it used a lot in old movies, people communicating over great distances with dots and dashes
If the signal is bounced off the ionosphere how does the person receiving the message know which message is theirs?
I’m assuming many messages were sent during the war … with all those messages bouncing around how did we zero on the one specifically for the receiver ?
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I am a licensed and practicing RadioTelegraph operator. There are still some ship to shore radiotelegraph services, most notably KPH just north of San Francisco. (https://www.radiomarine.org/)
Telegraph is simply on or off. It’s a binary code, read by humans. A light switch can be used as a telegraph. Matter of fact, we mariners are still required to be able to send Morse via flashing light as a rudimentary (and secure!) signaling method.
When you hear a tone with the telegraph signal, it’s being sent over a radio link In addition to using callsigns, we use different pitches (frequencies). Radio receivers can be tuned to listen to only one pitch at a time.
Ever heard one of those machines that shifts the pitch of a voice higher or lower to disguise it? It’s similar to what we do with telegraph by shifting that signal all the way up, past human hearing, past dog hearing, into the radio spectrum where it can be amplified (made louder) and sent long distances – Think thousands of miles. A radio telegraph receiver is just a machine that shifts that pitch back down to a few hundred hertz where a person can easily hear it.
If I switch to a wider filter, one that can receive a human voice, I can hear several telegraph signals. They’re all at different pitches though. I’m trained to be able to pick one out, focus on it, and decode the morse. It’s a lot easier with a narrow filter picking up only a single signal, though. In the early days of radio, it wasn’t possible to be so selective and operators had a harder time of it.
Happy to answer your questions! I love radio and Morse Code.
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