Ham Radio News: Rise of the Communications Satellite

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PHOTO: MADELEINE MACDONALD
Copthorne Macdonald, the inventor of slow-scan television, sees both great opportunity and great risk in the use of communications satellites for ham radio transmissions.

The earth is, of course, round, and radio signals travel in straight lines. How, then, can transmitted signals ever arrive at receivers on the opposite side of the globe?

Well, as I’ve mentioned in previous columns, Mother Nature very kindly provided the earth with an imperfect, intermittent–but extremely useful–radio mirror that’s located about 200 miles above us. Called the f2 layer of the ionosphere, this “reflector” bounces certain high frequency (HF) radio signals back down again. Short wave radio–including HF ham radio–can cover long distances because it’s able to utilize this phenomenon.

You see, while radio waves won’t follow the earth’s curvature, they will bounce back and forth between the ionosphere and earth, and in this manner travel around it. Thef2 layer does a fair job of reflecting the 27 MHz of spectrum space in the HF range, but it’s subject to disruption by solar storms and so forth. Also, this natural “mirror” rarely reflects the 270 MHz of available spectrum in the VHF range, and never bounces back the 2,700 MHz in the UHF or the 27,000 MHz in the extremely high frequency (EHF) range.

Satellite Reliability

In the 1960’s and 70’s, a new technology emerged and evolved: the communications satellite. Such earth orbiters are simply radio relay stations located far above our planet. They receive signals from stations on the ground and retransmit those signals back again.

  • Published on Mar 1, 1979
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