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.
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:
It seems that each new technology automatically offers both advantages and disadvantages. Every "advance" raises new dangers, just as it brings new benefits, and communications satellites are a perfect example of this two-sided technological coin.
The advantages of orbiting relay stations are clear. For example, the width of radio spectrum that can be relayed by satellite is more than 1,000 times that which the ionosphere can handle. Ten thousand voice channels are about the limit for the HF spectrum, and the ionosphere has defects which make it totally unsuitable to relay conventional TV signals. But the chunk of spectrum which satellites can transmit is over 10 million voice channels wide. And that's enough to accommodate 5,000 TV channels! Furthermore, TV signals can be relayed as clearly as voice signals. And, satellites—once they're up and operating—are much more reliable than is the ionosphere.
Naturally—in order to take advantage of these "plus points"—corporations and governments have been launching communications satellites by the score. In fact, placing these orbiters has become one of the routine activities of the residual space program and long ago ceased to be news. The modem signal senders not only carry telephone conversations and TV programs around the globe, but have also been used to carry education and medical advice to people in rural areas.
Furthermore, while military communications and the spread of mindless television programs may alarm us, most of the uses of satellites seem commendable, we recall that the telephone was cited by Ivan Illich as an example of a humanly liberating, "convivial" tool. And no one would criticize the transmitting of literacy and lifesaving advice to remote places. What, then, are the negative factors?
Cost is one, although—with 20 years of expensive space research and development already paid for—the price of building and launching satellites has dropped to fairly reasonable levels. (In fact, these "birds" are by far the cheapest method of solving many of our difficult communication problems.) No, the prime negative in all this is not cost. IT'S THE DANGER INHERENT IN CENTRALIZED CONTROL. Let me explain this hazard by using the example of ham radio.
I'm one of several hundred thousand hams dotted around the globe who are equipped with personal HF radio sending and receiving sets. Each of us is capable of making direct contact (via the ionosphere) with many similarly equipped operators. Now, the reliability of this system leaves something to be desired. Mother Nature doesn't always provide a perfect radio mirror whenever we want it, but we do always know that she will eventually come through. If a solar storm has dirtied the mirror today, we can be pretty sure that it will be clean again tomorrow or the next day. So, as long as my equipment works—and the other fellow's does, too— we will be able to communicate with each other sooner or later.
But what if ham radio converted to satellites? Let's assume that—over the years ahead—all of us hams got rid of our HF gear and switched to a satellite-relayed communications system. We could then talk to each other with perfect clarity, and our communication would be 100% reliable. That is, until the day when someone decided that such communication was no longer desirable and turned the satellite OFF!
That's the rub! Every communications satellite is built in such a way that those corporations, etc. who set it up can also turn it off. All they have to do is send up a coded radio signal from their ground station to the satellite! Where would that leave hundreds of thousands of hams? We'd be totally out of touch with each other and absolutely powerless to do anything to reestablish communication.
There are amateur radio satellites these days, and such "space stations" are interesting and useful communication tools. In fact, in a future column I plan to go into this facet of ham radio more fully. But total reliance on satellites is a risky business. Sure, governments can always decree ham radio operation illegal as they did in World War II. This kind of legislation, however, wouldn't necessarily mean that the "switch" is really off. During the war—particularly in Norway and Holland—HF ham equipment found its way into the hands of the resistance that opposed the Nazi occupation. The basic capability to communicate still existed. With a turned-off satellite-based system, there would have been no such capability.
On a saner planet—where all governments truly represent the interests of the world's people—a satellite-based radio system would make perfect sense. Perhaps we must assume that the world will grow saner, and go ahead with such a system anyway. Or maybe we should go ahead but continue to use ionospherically propagated HF radio as a backup.
If you have further thoughts on this subject, drop me a line. It's a matter we shouldn't ignore.
Cop Macdonald (VE1BFL)
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