V. DIGITAL RADIO MODES Cop Macdonald writes in "Mother Earth News" no. 81: "Radio amateurs, like many other people these days, are buying home computers. And regardless of how many additional uses he or she might plan for the machine, a ham purchaser almost always wants it to be part of a system of communication. "In theory at least, personal computers and ham rigs can be interconnected, and the combination can then be used to transmit and receive text by radio. Three types of codes are commonly employed for these transmissions: ASCII (standard computer code), Baudot (normal teleprinter code), and Morse (dots and dashes). "However, in this case what seems to be simpler in principle turns out to be not so easy in practice. For one thing, obtaining all the necessary bits and pieces of equipment--and integrating them into a smoothly functioning system--requires knowledge and patience. "If you already have a ham radio transceiver (or a shortwave receiver) and a home computer, you have two of the four elements needed to create a working system. The third component is a piece of interface hardware. This unit functions as a kind of translator, converting the 1's and 0's of computer language into the changing audio tones of radio language, and visa versa. Finally, you'll require the appropriate software. Just as a home computer needs game software to play games and accounting software to do bookkeeping, it will also need communications software in order to communicate. The overall problem is further complicated by the fact that there are many different makes of home computers...each with its own peculiarities." RTTY RTTY is used for a great many purposes. Military communications, embassies, and other government agencies rely on it--although such transmissions are usually coded. Easier to monitor are international meteorlogical transmissions, ships at sea, and aeronautical communications. RTTY is an especially fast growing mode on amateur radio. Transmissions can be heard, for example, in the 80 meter band between 3580 and 3600 kHz and in the 20 meter band between 14080 and 14100 kHz. Possibly the most exciting RTTY transmissions are from international news agencies. Though much of their networking is today carried out over cable and satellite links, most agencies still rely on shortwave to reach some subscribers, or as a back-up. It can be very exciting to see news copy on your screen, or coming off your printer, knowing that the same news is being printed at the same second at newspaper offices and radio and television stations around the world. While the "Big Four" agencies--AP, UPI, Reuters, and AFP--are well represented on shortwave, it's often more exciting to monitor news reports from smaller agencies, such as Cairo's Middle East News Agency and Cuba's Prensa Latina. The Yugoslavian news agency Tanjug relays the Non-aligned News Pool. The latest amateur radio use for RTTY is the mailbox. This is similar to the computer bulletin board (see Chapter VII). Radio amateurs with RTTY capability can transmit a signal to turn on the mailbox, leave messages for other amateurs, and read messages to themselves. There are a number of inexpensive mailbox software packages on the market, advertised in amateur radio magazines. Mailboxes are increasing, especially in the United States. In Europe, we've noted a West German mailbox operated by DF3IX on 3584.5 kHz and an Italian mailbox just below 14100 kHz. The latest digital mode is packet radio (see below). Packet mailboxes and bulletin boards are flourishing, especially in North America, offering virtually all the features of over-the-telephone systems. If you're interested in building your own RTTY interface, Jim Grubbs published a schematic for a simple interface in the April, 1985 issue of "Commodore User" magazine, as well as a short program for using the interface to monitor morse code. The following month's issue contained a follow-up article with an RTTY program. The November, 1985 issue of "Antic" magazine carried an article on using an Atari computer for RTTY and AMTOR. Another article included a BASIC program for receiving morse code as well as a diagram for an interface. Commercial RTTY Interfaces There are a great many RTTY interfaces and software packages on the market, for a variety of computers. Almost all of them work with the Commodore 64 computer, which seems to be the most popular among radio enthusiasts, as well as probably the most popular home computer in the world. Most packages are for both sending and receiving and are thus more expensive than simple receive-only units. Many of these units also include AMTOR, a self-checking RTTY that sounds on the air like a cricket chirping. Perhaps the three best-known interfaces come from the American companies Kantronics, MFJ, and Microlog. Kantronics (1202 E. 23rd Street, Lawrence, Kansas 66044, USA) offers at least four terminal units from the $100 "Challenger" to the $270 "Interface II" and $360 "UTU-XT". The units can be used with a number of different computers, and Kantronics sells software that can be used with Apple, Atari, Commodore, IBM, Kaypro, Radio Shack, and Texas Instruments machines. Some of the software programs also include AMTOR. There is also a receive only unit, with software cartridge for RTTY and CW for the VIC-20 and Commodore 64 computers, called the "Radiotap", for $200. MFJ (P.O. Box 494, Mississippi State, MS 39762, USA) also sells interfaces and software, ranging from the MFJ-1224 standard interface ($100) to the MFJ-1229 Deluxe model ($180)(which includes a tuning indicator--the company also sells a separate tuning indicator for $80). These interfaces include AMTOR and will work with Apple, Commodore, Radio Shack, Atari, and Texas Instruments computers and will run software from AEA and Kantronics as well as MFJ's own. MFJ sells a morse only cartridge for the Commodore machines for $40 as well as an RTTY/ASCII/CW/AMTOR Commodore cartridge for $70. There is also a receive-only interface (MFJ-1225) compatible with the computers above for $70. Microlog (18713 Mooney Drive, Gaithersburg, MD 20879, USA) has gone beyond the other companies making RTTY equipment. Most systems involve two elements--a hardware interface and separate software. Microlog has developed RTTY units for the Commodore computers in which both interface and software are included on the same cartridge. The single unit plugs into the cartridge port and cables run from the unit to the receiver or transceiver. The AIR-1 costs $199. There is a more advanced unit that includes AMTOR for $280. Microlog has also developed a simple receive-only interface for the Commodore 64 computer that is just an ordinary-sized software cartridge, for $64. We've tested the unit and found it very good indeed. The only drawback is that perhaps too many of the transmitting features are still included, including a splitscreen that has to be turned off. Microlog says the transmitter features serve as a simple word processor for writing letters, but it's very simple for such functions. We also found that the cartridge could slip off the expansion board we tested it on. One of the big advantages of the unit is the on-screen tuning indicator, the same as that used in the AIR-1. It is very useful in tuning in RTTY signals. Microlog also offers a cartridge called "Morse Coach" to learn morse and a cartridge called "CW-1" to send morse to a transmiter using the computer keyboard. Both are for the Commodore 64 only and both cost $50. A cassette with RTTY software for the AMSTRAD CPC 464 computer has been advertised from: Scarab Systems 39 Stafford St. Gillingham, Kent ME7 5EN ENGLAND Those who are more interested in experimenting may be interested in a Commodore 64 interface from Computer World (Hilvertsweg 99, NL-1214 JB Hilversum, the Netherlands) called the COM-IN 64. It consists of two circuit boards, one which plugs into the cartridge slot of the computer, the other into the user port. A band cable connects the two. The unit is also supposed to be able to be connected to a telephone line as a modem, and is also supposed to receive slowscan TV (SSTV) although we had no success with the unit we tested. COM-IN is available for about $200. G1FTU has developed an ingenious cassette software program for the Sinclair Spectrum that permits RTTY operation without an interface. The computer's cassette input and output ports are connected directly to the receiver or transmitter. This unit is being sold in Sweden for SEK 159 from Chara Electronics (P.O. Box 119, S-813 00 Hofors, Sweden). It should also be available from Pearsons Computing (42 Chesterfield Road, Barlborough, Chesterfield, Derbyshire, England). There is a similar SSTV program. Shuttle SSTV With a VIC-20 Copyright 1985 by Jim Grubbs When I was a young novice of age 11 the then fledgling amateur radio satellite program held me completely in awe. It was to be some number of years before I got the chance to operate my own earth station, but in the meantime I became thrilled with every launch into space. A few years later, I found myself regularly monitoring the recovery network based around the world for the Gemini flights. What I didn't suspect then was that one day I would be able to hear astronauts actually transmitting on the amateur radio bands and at least have a chance of actually talking to them! All of that's fine, but what on earth does it have to do with computers? Well, what I also didn't know was that this marvelous box called a VIC-20 would later enter my life and that with it I would not only be able to track the astronauts, but also SEE them! During Tony England's recent Space Shuttle operations, he operated slow scan television, sending back pictures from space on the two meter band. But special receiving requipment normally costing hundreds of dollars was needed in order to view the pictures. That is, unless you own one of several low-cost micros. While the shuttle flew overhead one night in July, 1985, I sat in my shack watching the pictures being translated by my VIC-20! Other amateurs used Radio Shack color computers and even an IBM or two decoded the signals. The secret is in a low cost interface and an appropriate program. Check the magazine ads for slow scan programs for the IBM and Apple computers. For the VIC-20 and C-64, there is a package from: vicComm Box 5491 Duke Station Durham, NC 27706 USA Information on a program for the Radio Shack color computer can be obtained by writing: QCD Marketing Services PO Box H Lowden, Iowa 52255 USA FAX Another digital mode that lends itself to monitoring with the help of a micro-computer is facsimile, or FAX. The most interesting application is for weather maps from satellites, such as the American NOAA series (WEFAX). Mike Stone, editor of "SPEC-COM", has produced software for the Radio Shack Color Computer which will allow reception of WEFAX signals, such as can be heard on the NOAA satellites on 135.5 MHz. Instead of using a hardware interface, the program allows WEFAX reception "with joystick control" (which we assume means interfacing through the joystick port). WEFAX 1.1 will receive 60, 90, and 120 lines per minute facsimile in full screen format. Hard copy print-out is also possible. For more information, write to: SPEC-COM Membership Services Department, P.O. Box H., Lowden, IA 52255, USA. ("Monitoring Times") The British magazine "Practical Wireless" carried a series on monitoring weather satellites, beginning in September, 1985. The December, 1985 issue reviewed a system from the British company Timestep. This company sells receivers, interfaces and software for using BBC Micros for monitoring weather satellites. Timestep Electronics Ltd. Wickhambrook, Newmarket Suffolk, England Packet Radio Copyright 1985 by Jim Grubbs What's like radio teletype but won't print on a teletype machine? What's based on telephone computer communication techniques but doesn't connect to a telephone? The answer is packet radio. World wide communications links for computers often use a technique called packet transmission. The information to be sent is divided into many small groups of characters. Each packet as these groups are called contains addressing information and error correction information. The result is that packets from many different locations can share the same communications channel and all arrive at the proper destination error free. Amateur radio operators throughout the world have adapted this system to radio transmission. Rather than using telephone links transmission techniques like those used for radio teletype are employed. Most of the activity occurs in the VHF spectrum with much of it done in the 144 MHz band. On VHF 1200 baud channels are the norm, while on shortwave frequencies slower rates must be used in order to obey bandwidth limitations. Experimentation is being done in the UHF range that allows channels to exchange data at rates of 19,200 baud. One of the most unique aspects of packet transmission involves the addressing that is available. For example, by using packet radio on the 2 meter ham band I can use my ten watt FM transceiver to repeat to a special digital repeater located several miles from me. With the proper addressing my signal is sent on to another repeating station about 50 miles to the northeast. There the signal is picked up by a wide area repeater (a super repeater if you will). The signal is relayed into a station just a few miles from my dad's house. With a station similar to mine, he will receive my messages approximately 30 seconds to one minute after I send them. There are even plans for a packet satellite. Packet Radio Terminals The protocol standard coming into use for Packet Radio was developed by amateur radio operators in Tucson, Arizona, and is called TAPR (Tucson Amateur Packet Radio), as is the organization that has sold kits for the necessary modems (TNCs) for interfacing computers and transceivers. (Ordinary telecommunications software can be used for packet.) They have ceased offering their TAPR2 kits and have licenced a number of manufacturers to produce packet radio controllers. The least expensive packet radio controller is being sold by MFJ. Their model MFJ-1270 costs $130. It will work with any computer with a RS-232 serial port and a terminal program. For the Commodore 64 or 128 or VIC-20 there is an optional starter pack for $20, which includes interfacing cable, and terminal software on tape (MFJ-1283) or disk (MFJ-1282). Kantronics offers a "Packet Communicator", which features a direct TTL connection for easy hook-up to the VIC-20 and Commodore 64/128. It includes both Bell 202 and 103 tones for both VHF/UHF and HF work. Selected retail price US$ 219. The "On Line" column in the October, 1985 issue of "QST" describes a packet radio interface for the Apple Macintosh computer called MacPacket/TAPRterm. For more information contact: Jack Brindle, Brincomm Technology, 19451 Gulf Blvd. No. 503, Indian Rocks Beach, FL 33535, USA. The AEA PK-64 Copyright 1986 by Jim Grubbs The PK-64 is a combination hardware/software addition designed to be used exclusively with the Commodore 64 and 128 computers. The resulting marriage between the computer and the PK-64 allows you to monitor most all of the digital traffic on the short wave bands today. It is also designed for transmitting, but at a suggested retail price of $220 in the U.S. it's sure to become a favorite with the SWL community as well as amateur radio enthusiasts. Everything you need for copying morse, RTTY, TOR/SITOR and AMTOR, ASCII and even packet radio are resident in this one unit! Software wise, the PK-64 makes use of a modified version of the very popular and versatile MBATOR package sold by AEA for the last several years. The terminal unit used in the PK-64 uses the same technology found in the CP-1 computer patch. The serious DXer will want to add the HFM--high frequency modem--to the basic unit. It offers much better filtering than the standard unit and includes an excellent and easy to use tuning indicator. With the PK-64 in your radio shack you will be equipped to monitor a wide variety of digital signals. It is a truly outstanding value and I highly recommend it. For further information write to: Advanced Electronic Applications, PO Box C-2160 , Lynnwood, Washington 98036.