WEATHER MAPS FROM SPACE
BY CHARLES JACKSON , ANTIC TECHNICAL EDITOR
Tune in a weather satellite and downlink a few pictures from space! A standard shortwave radio plus this issue's WEFAX Decoder software and WEFAX Interface board are all that your Atari needs for receiving and displaying Weather Facsimile pictures from the satellites of the U.S. and other nations, as well as facsimile photos from newswire services.
This Weather Facsimile system is the most ambitious project ever published by Antic. It required more than six months of intensive research, programming and hardware development. But the result is the most versatile and friendliest weather satellite software available for the Atari 8-bit and ST computers.
The reason this project turned out to be so demanding is that its success depends on many factors--including software, hardware and the forces of nature. Especially important are what type of radio and antenna you use, and the area you live in.
You need a shortwave radio capable of receiving SSB (single sideband) signals. Inexpensive "all-band" portables with telescoping antennas will not suit our purposes. We developed these programs using a Radio Shack DX-302 attached to a 25-foot long- wire antenna. But for good results, you should use the best receiver and outdoor shortwave antenna you can afford.
Also, even if you type in the program perfectly and build the interface circuit without a hitch, you could be out of luck if you live in an area with poor shortwave reception. WEFAX signals are clearest in suburban and rural areas. If you live in the center of a large city, you may have trouble receiving a clean WEFAX picture.
Antic technical staffers (from left) Bill Marquardt, Charles Jackson and Patrick Bass discuss methods of adapting the 8-bit WEFAX program to the 520ST.
Before you can use the Decoder programs, you'll have to build the WEFAX Interface described in this issue. The interface is a simple circuit that can be built for under $20.
Listing 1, WEFAX.BAS, is a BASIC program which creates the WEFAX.EXE machine language program for Atari 8-bit computers. Antic Disk subscribers will find a copy of WEFAX.EXE on the monthly disk. Copy WEFAX.EXE to another disk and rename it AUTORUN.SYS, then follow the instructions in the accompanying articles.
Listings 2 and 3, FAX.M65 and FAXA.M65, contain the MAC/65 source code for WEFAX.EXE. You do not need to type in these listings to use the WEFAX program. Listing 4, WESIM.BAS, is a BASIC program that simulates a WEFAX signal. If you've never heard a WEFAX signal, this program will create one for you. Listing 5, WETST.BAS, is a BASIC program that helps you test your WEFAX Interface circuit.
The ST version of WEFAX Decoder is WEFAX.TOS and you'll find the article explaining it in this issue's ST Resource section.
Finally, Antic would like to thank all the people who helped us with this project, including: Dr. Ralph Taggart, Dr. Marty Goodman, CompuServe Vice-President Sandy Trevor, Gary Sargent (creator of the first WEFAX program for the Atari), Michael Schuster, Vic Moore, Jim Grubs, Chris Elmquist and Wayne Day. Special thanks to the staff of the San Francisco Area Office of the National Oceanic and Atmospheric Administration.
If you want to learn more about Weather Satellite transmissions, here are some of the best sources to get you started:
The New Weather Satellite Handbook, by Dr. Ralph Taggart. This is the definitive text on WEFAX. Formerly out of print, an updated edition of this popular book is available from the author for $12.50. Add $2 for orders outside the U.S. Write: Dr. Ralph Taggart, 602 S. Jefferson, Mason, MI, 48854.
Hidden Signals, Second Edition, by Thomas Harrington and Bob Cooper Jr. Although its discussion of weather satellites is rather brief, this book is packed with information about satellite television, AP-UPI satellite relays, stereo down- links, teletext and videotext service. If you want to learn more about communications satellites, this book belongs on your shelf. $19.95, Universal Electronics, Inc., 4555 Groves Road, Suite 13, Columbus, OH, 43232. (614) 866-4605.
The Shortwave Facsimile Frequency Guide, $14.95. Universal Electronics Inc., 4555 Groves Road, Suite 13, Columbus, OH 43232.
Weather Fax Guide. Infonnative free catalog from Atlantic Surplus Sales, 3730 Nautilus Avenue, Brooklyn, NY, 11224. (718) 372-0343.
Weather Satellite Fact Sheet. Free leaflet from Radio Nederlands, P.O. Box 222, Hilversum, The Netherlands.
Operating a Weather Satellite Ground Station. Free from NASA Educational Programs Office, Code 202, Goddard Space Flight Center, Greenbelt, MD 20771.
If you're a CompuServe subscriber, you can also find WEFAX information in the HAM radio SIG (type GO HAMNET) and in the Radio Shack Color Computer SIG (type GO COCO).