Tuesday, August 30, 2005

Amateur Radio Beep Beep. I know, dear reader, you have been thirsting for another post on amateur radio, so here is one on the topic of amateur radio beacons.

As you may recall, one can communicate by radio on certain frequencies with those who live below the horizon. This is because of the ionosphere, layers of ionized atoms that surround the earth. Those atoms are ionized when the UV radiation from the sun hits them, knocking off electrons and creating charged particles. When one transmits a radio-frequency (RF) signal with a given wave-length, that signal will radiate toward the horizon, "bounce" or refract off the ionosphere, and end up on the other side of the horizon. If the part of the ionosphere in question is high enough, then the RF signal will bounce pretty far. After it comes down on the other side of the horizon, the radio signal may bounce off the earth and be sent up into the ionosphere a second time, and so on, all the way around to the other side of the earth or maybe all the way around to where the signal originated. This bouncing and refracting off the ionosphere is called propagation. But you knew that.

Sometimes, though, the sun doesn't do its job and no propagation on a given band is taking place. Its a bit like the weather. (One part of the amateur radio hobby is devoted to keeping track of and forecasting propagation. I know you would like to hear more about that sort of thing, but you will have to wait for another post, unless I get a life in the meanwhile, in which case you will never hear from me again.)

So here I am, turning on my radio, and I hear no one. No signals are coming in. Hhhmm, I might say, the band is "dead" or "down". Propagation is not working. Bad sun, bad, bad sun.

Or maybe not. Maybe everybody else went to the beach. Or maybe everyone else is listening too. How does one know?

Well, there is another part of the hobby, where people set up radio beacons. A beacon is a transmitter, usually run by a computer program, that transmits a signal every so often on a given frequency and gives its call sign or identifying letter/number combination. If you are tuning around and pick up that signal and you know where that transmitter is, then you know that the band is not dead. You know that propagation is working, unless the beacon is located next door and not over the horizon.

The Northern California DX Foundation, with the help of an agency connected with the UN, has set up a network of beacons all around the world. These beacons coordinate their signals and each beacon transmits for, say, 10 seconds, one after another, on the same frequency. So, you tune the receiver to the subject frequency and then listen. It is unlikely that you will hear all the beacons as the signals emanate from around the world. But unless the band is completely dead, you will hear one or more.

For example, recently I tuned to the beacon on 20 meters, a popular amateur radio band. I heard the beacon at the UN in New York, then the beacon in Northern Canada, then the beacon in Hawaii, and then the beacon in Venezuela. During the rest of the cycle, I heard nothing, even though the beacons in other parts of the world were taking their turns.

Furthermore, each beacon in this network does not simply broadcast its call sign, it also follows its call sign with a series of dashes (or "dahs" as we CW operators say). The first dash is broadcast at 100 watts, the second at 10 watts, the third at 1 watt, and the forth at .1 watt. This will give you information not only on whether there is propagation on the band, but also how good it is. I can usually hear at least the first two dashes.

Now isn't that just about the most interesting thing you have learned all day?

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