Ham Radio News: Rise of the Communications Satellite

The communications satellite could be a great boon to ham radio uses, but also create a great vulnerability to those who become dependent on it.


| March/April 1979



copthorne macdonald - communications satellite.jpg

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.


PHOTO: MADELEINE MACDONALD

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.

And, unlike the ionosphere—which can reflect only a limited range of frequencies—communications satellites can be designed to relay any frequency. Now, instead of long distance transmission being limited to that measly 27 MHz of spectrum contained in the HF range, the almost 30,000 MHz of VHF, UHF, and EHF spectrum can also be relayed to distant places.

In a recent letter, John J. Stewart (WCEY99B) refers to that ample bandwidth which is a characteristic of satellite systems. He wonders if communications satellites might not be the answer to disseminating ham radio news and establishing widespread people-to-people radio communication with little or no government regulation. He suggests that we use this column as a forum to air the issue. You've got a good idea there, John! So here goes:





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