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A post for the nerds: Radioteletype

The radio is tuned to 14.08128 megahertz. This is in the 20 meter ham radio band in a frequency range normally reserved for radioteletype stations. Signals on the 20 meter band, by the way, travel farthest when the sun is overhead. During the day the earth’s ionosphere is energized by solar radiation, making the ionosphere reflective to 20-meter signals. The signals go up 200 miles or so, then bounce back down to earth, far from the point of origin.

This photo was taken during a radioteletype transmission. The meter is saying that 30 watts of power is being sent to the antenna (left needle on 30). Because the antenna is tuned for this frequency, the antenna is not rejecting and thus reflecting any of the transmitter’s power (right needle on 0). In other words, there is no standing wave on the antenna feed line. The standing wave ratio (SWR) is 1:1.

Instead of mechanical teletype machines, computers are now used to encode and decode radioteletype signals. This is a program for Macintosh named CocoaModem.

A few days ago I posted an item about Teletype machines and a mode of communications called radioteletype. Radioteletype is obsolete commercially, but it remains an excellent means of communication on the high-frequency (short wave) radio bands. When I posted last week, I had not yet got around to setting up radioteletype on my apparatus at home. As of today, it’s working.

Digital (as opposed to voice) signals were booming in from Europe today during the afternoon, when the sun was over both Europe and the United States. I was still working on setting things up and adjusting things, but I did talk with two stations in Cuba — CO8LY and CO2NO. I talked with CO2NO using 20 watts of power on a new digital mode that is a relative of radioteletype — PSK31. I talked with CO8LY via radioteletype using 30 watts of transmitter power.

You might wonder how 20 or 30 watts of transmitter power could travel from North Carolina to Cuba. Two reasons, basically. For one, the power is focused into a narrow beam of bandwidth, far too narrow to carry the human voice, but enough for a relatively slow digital signal such as radioteletype. For two, the earth’s atmosphere is very transparent to radio waves. Or, to say it a little differently: It would be more difficult to talk with someone in Cuba using a microphone and voice communications. “Narrow” digital modes such as radioteletype and Morse code carry less information per second, but the power used travels much farther.

I never use more than 100 watts.

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