Ham Radio Allows Digital Communication

An amateur ham radio allows digital communication across the world.
By Copthorne Macdonald
November/December 1983

The AMSAT (Amateur Satellite Corporation) is the group through which a host of radio amateurs and volunteer space technologists have worked to produce the OSCAR series of ham radio communications.
Photo provided by Fotolia/Khunaspix


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The author of this column is the inventor of slow-scan television . . . a method of amateur radio transmission that allows ham operators to both hear and see each other during short wave broadcasts.

In what may be the finest example yet of high-tech volunteerism, two grass-roots organizations are cooperating to design, produce, and launch a packet radio satellite by mid-1985: AMSAT (Amateur Satellite Corporation) is the group through which a host of radio amateurs and volunteer space technologists have worked to produce the OSCAR series of ham radio communication satellites. And VITA (Volunteers in Technical Assistance) is an association of 4,000 unpaid workers who offer their specialized skills to facilitate projects in developing countries. The two forces are now focusing jointly on the establishment of PACSAT, a low-altitude satellite that will bring worldwide digital communication within the financial reach of individual Western hams, as well as those in impoverished Third World countries.

VITA is known throughout the developing world for its emphasis on village technology . . . the sort of practical engineering that E.F. Schumacher advocated in his book Small Is Beautiful. VITA workers have helped people all over the globe to find simple, low-cost ways to provide such basics as food, water, and shelter. Why, then, is VITA involved in a high-tech project encompassing satellites, microelectronics, and digital communication?

Well, that interest actually has several roots. One is VITA's own communication problem, which is caused by the fact that, although most VITA volunteers live in North America, the vast majority of the organization's projects are in other parts of the world. At present, almost all of its dealings between technicians and their contacts in developing countries are by slow (and often unreliable) international mail. So a two-way system that could deliver messages in just hours, rather than weeks or months, would greatly enhance the group's effectiveness.

Also, many people in the Third World are calling for leading-edge technology - wherever its use seems appropriate - but the cost is often prohibitive for them. To help sort out its own role in this area, VITA recently held two workshops on the subject of microelectronics and development, and among the many possibilities that emerged from these gatherings was the idea of a satellite that could act as a "flying mailbox" . . . picking up messages as it passed over one part of the world, and delivering them as it passed over others. Discussions about a joint VITA/AMSAT project followed shortly thereafter.

The new satellite, in fact, is a natural next step for AMSAT. Although each OSCAR satellite launched to date has been more technically sophisticated than the one before, all have been basically direct repeaters, receiving a signal on one frequency and simultaneously retransmitting it on another. A major disadvantage of this setup is that the satellite must be within line-of-sight radio range of both the sending and receiving stations during the entire transmission period. Thus, the maximum range of the system is limited to just a few thousand miles, making it impossible to communicate with a station on the other side of the world.

But PACSAT will differ from the OSCAR series satellites in three major respects: It will travel in a sun-synchronous polar orbit (which insures that the satellite will be accessible from every point on earth at least twice a day, at the same time every day) . . . it will receive and send via short packets of digital code . . . and it will have one million bytes (characters) of on-board solid-state memory for storing messages. These features, working together, are what will make PACSAT behave like a flying electronic mailbox.

Picture the following scenario: Say that Gary Garriott (WA9FMQ), coordinator of VITA's microelectronics activities, wants to send a message from his station in Washington, D.C. to another one in the South Pacific. Gary first types his dispatch into a small personal computer, which places the information in digital storage . . . ready for the rapid transmission that the satellite requires. During a satellite pass over his city, Gary makes VHF radio contact with PACSAT, and starts the transmission procedure. The first data packet-containing part of the total message-blips up to the satellite, along with a special code that lets the system know whether or not the packet was received correctly. If it detects an error, PACSAT asks for a repeat . . . otherwise, it requests the next packet. In this manner, Gary's dispatch is reconstructed, packet by packet, and stored in the satellite's memory, waiting to be picked up. As the satellite continues to orbit over the earth, eventually -say, during a pass over the South Pacific -the intended recipient radios up to check for messages. PACSAT responds by pulling Gary's message out of memory, packetizing it, and sending it down.

PACSAT, like the OSCAR satellites, will be inexpensive to produce, launch, and use, thanks to a wide variety of nonmonetary contributions: volunteer labor from highly skilled people, materials donated by aerospace and electronic companies, and a free launch (PACSAT will probably go along piggyback with some "paying" cargo). And user cost won't be high, either. The low-altitude orbit permits inexpensive VHF ham gear to be used for communication from the ground. The antennas required will be simple configurations of aluminum tubing or wire . . . not big parabolic dishes. And even the digital hardware needed by each ground station doesn't cost much.

PACSAT will be an experiment in amateur radio, but it has obvious ramifications beyond just ham applications. Quite possibly, additional satellites of similar design but operating on commercial and government frequencies-will be sent up eventually. I find all this very exciting. Once again, radio amateurs are significantly advancing the art of communication. Volunteerism is alive and well. There are things besides money that motivate people!

Two Computer Newsletters

Reset: Notes on Alternative Informatics is concerned with the human side of computers and electronic information transmission. Mike McCullough, Resets editor, recently sent me a copy of their issue 5, a 16-pager that contains information on a variety of subjects: groups such as Computer Professionals for Social Responsibility and Community Communication Services .. . the possible health hazards of CRT terminals . . . Apple's Community Affairs Grant Program . . . and lots more, including six book reviews.

Journal/20 is a newsletter for VIC-20 users. Edited and published by Mike Apsey (WSVKC), the 12-page publication comes out every two weeks. It's loaded with programming hints, ads for VIC-20 peripherals and software, and articles on how to get the most out of your VIC. Mike reports that 80 percent of his 600 subscribers are U.S. hams!

New Directions Radio is an international network of radio amateurs concerned with those ways of using ham radio (and related modes of communicating that promote our own growth as individuals, and that we perceive as helping to create a more aware, more caring, and more responsible human society.


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