FI2: Computers and Radios by Illusion
Freedom Issue 2, February 28, 1993
File 4/7
COMPUTERS AND RADIOS
By Illusion
PREFACE
Well, first of all, I am by no means an authority on this subject. I am just interested in it, and have decided to share with others what I have learned so far. I am not going to list any sources because I simply can't remember any. I did not originally intend to write anything about this, but I figured that maybe someone else might find it interesting as well. The information used in this article was not deliberately or specifically obtained from any particular sources. It is a compilation my personal knowledge and experience on the subject. A long time ago, I heard that it was possible to transmit data through the so called "airwaves". This seemed very interesting to me, so over time, I've learned about it.
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A huge amount of data is available throughout the radio frequency spectrum. To access it, you need a radio receiver and a computer. Just like we have protocols, there are special protocols used on the airwaves. Equipment, software, and instructions are all available from several sources including ham radio groups. However, there are other ways to go about setting up a "station". I would recommend buying all of your needed equipment used.
I have not intended this article for use by the absolute beginner in radio data communications. If you are interested in the equipment, the basic instructions/techniques, or a general overview, then contact a local amateur radio club. They will be able to provide you with all of the information that you require -- usually at no cost.
First you will need a receiver. It must at least cover 100kHz to 30 MHz and have AM, USB, and LSB. (USB=Upper Side Band, LSB=Lower Side Band) The better the radio, the easier it will be to find and receive the data. Now, you need an antenna. Don't expect to use your old cheap CB whip. I would recommend what is known as the "active dipole". It is usually small and has 2 lengths of wire that are tied parallel to the ground. Of course you want this as high as possible and far away from the computer to ensure good reception and little interference.
Next comes a computer. Just about anything will do. Even an old VIC-20 would do the job, but more software is available for PC's. Now you need an interface or a radio modem. There is a huge variety of these, but you need one that fits the industry standards...the best idea here would be to contact a dealer. You can probably find a good model for a relatively inexpensive price.
OK, I'm not going to go into the special protocols here. You can find this information very easily in instruction manuals and books. What you want are some frequencies! Before you try listening in, don't be surprised if you see silly messages or meaningless characters. They are used just to sort of reserve a frequency. An example would be: RYRYRYRYRYRYRYRYR... on and on until the station was sending something for real.
Here are a few where you are likely to find others talking (RTTY (Radio TeleTYpe)):
3950, 14090, 21090, 28090 ...or
at VHF/UHF frequencies: 144.6, 145.3, 432.6, 433.3
These are some where you may be able to find news agency transmissions (kHz):
3155-3400 3500-3900 3950-4063 4438-4650 4750-4995
5005-5480 5730-5950 6765-7000 7300-8195 9040-9500
9900-9995 10100-11175 11400-11650 12050-12330 13360-13600
13800-14000 14350-14990 15600-16360 17410-17550 18030-18068
18168-18780 18900-19680 19800-19990 20010-21000 21850-21870
22855-23200 23350-24890 25010-25070 25210-25550 26175-28000
29700-30005
Now you can know the news before it is broadcast, or sometimes, as it is happening. These are fun to listen to, but even more fun to broadcast to.
Use your imagination...
Well, one more thing that I wanted to cover (because it is so interesting), is satellites. I don't know very much about this, but I do know that you will need a scanner type of radio or a crystal controlled one. Some scanners have certain frequencies that are blocked out or don't work. These frequencies usually carry things like military information. With a little electronics knowledge, you will be able to easily fix these spaces as these are the really interesting freqs. You need a different antenna too. One of the ones that is sort of like a big horizontal "X" will work fine.
The general layout of the radio spectrum for satellites is as follows:
Amateur & Educational satellites:
144-146 MHz
430-440 MHz
Weather satellites:
136-138 MHz
Navigation satellites:
159-151 MHz
I heard that there are some that operate in the 1500+ MHz range, but I can't seem to figure out how to scan this high a frequency. The VHF/UHF scanner I was using couldn't go this high. I suspect that this may be where the "spy" and military satellites operate. However, I also would assume that any important data would be heavily encrypted.
A word of warning:
I am not sure about any laws regarding this subject, but I would be careful. It's easy enough to alter other peoples data and re-broadcast it with changes, but I would assume that this is illegal. It is extremely easy to receive a satellite weather image, and it is also very simple to change it and then send it out again. It might be fun to make there appear to be a hurricane approaching on the 6pm news, but they must have ways of tracking you down. So, once again, be careful. There are vast amounts of data riding the airwaves, and it is available for all to view, with the right equipment.
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The author takes no responsibility for the actions taken by any of the readers of this article.
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Illusion
