HamNet Packet Radio Tutorial - Part One --------------------------------------- by Scott Loftesness W3VS CompuServe 76703,407 Now that your SYSOP has begun experimenting in the exciting new world of Packet Radio, I thought it might be interesting to others here on HamNet to begin sharing a bit more of this new technology. . . Recently, I've uploaded a couple of news items which have highlighted commercial applications of packet radio techniques: the Genstar system being developed by Gerard O'Neil of Princeton University and the recently announced Motorola Portable Communications Terminal. I believe these to be just the first of many announcements we will see in the coming years as the packet radio form of digital communications finds even more commercial applications. . . In the meantime, we amateurs are blazing many new trails in this technology - from the simple TNC idea to the elegant PACSAT orbiting bulletin board system. Most of the success of the amateur radio packet efforts is due to a group of true enthusiasts scattered across the United States. Leading the way were our Canadian friends to the north who developed the original "Terminal Node Controller". Doug Lockhart and his friends in Vancouver developed an 8085-based TNC in the late '70's and its popularity spread quickly as they made available the PC board and parts kits. . . Pockets of packet interest rapidly developed in the Washington, DC, Tucson, AZ, and San Francisco Bay Area - to be quickly followed by new groups in St. Louis, New Jersey, and Southern California. The first ARRL Packet Radio Conference was held in October, 1981 in Gaithersburg, Maryland - and provided the first truly international amateur packet get together. Plans were reviewed - and ideas shared. One of the attendees, Den Connors, KD2S, moved off to Tucson to join a rapidly growing group of friends and formed Tucson Amateur Packet Radio. This energetic group began the creation of a completely new, "second generation" TNC - building on the best of the original work done in Vancouver. . . While the Tucson group was developing the hardware for a TNC, a group led by Tom Clark, W3IWI, became concerned about the lack of any kind of amateur standard as far as packet radio protocols were concerned. The original Vancouver protocol worked fine for a small group in a single geographic area - but clearly would not support the kind of growth in packet radio enthusiasts that was expected. In addition, the onset of the Phase IIIB amateur satellite and its packet radio repeater possibilites added impetus to the need to develop a new standard. . . Meeting in October, 1982, this group developed a new amateur standard called AX.25. The standard was completed just in time - it was incorporated into the original version of the Tucson (TAPR) TNC board in late 1982. Approximately 200 of the TAPR boards have been distributed nationwide - for extensive field testing of the hardware/software combination. This board has become a real hit - it worked beyond anyone's expectations and has created a tremendous additional interest in packet radio. The test phase is nearly complete - and will be followed by availability of a parts kit later this year for general distribution through the amateur community. By this time in 1984, amateur packet activities will have grown dramatically from the several hundred current experimenters to many more amateurs - and with exciting implications for new applications using the new technology. . . The TAPR TNC is a remarkable piece of equipment - and a truly elegant hardware/software design. We'll spend some time describing some of the details of this TNC. Much of this material is directly from the excellent manual which accompanied the beta test boards - and which is available from TAPR for $15 (PO Box 22888, Tucson, AZ 85734). . . The TAPR TNC is the result of a tremendous design effort by many people including Mark Baker, Marc Chamberlin WA7PXW, Pete Eaton WB9FLW, Chuck Green N0ADI, Dave Henderson KD4NL, Lyle Johnson WA7GXD, Dave McClain N7AIG, Dan Morrison KV7B, Margaret Morrison KV7D, and Harold Price NK6K, along with Den Connors. . . Very few terminals or home computers contain the hardware and software necessary to attach to, and control, an amateur radio. Compatibility between such systems could obviously be a problem. Because of this, extensive testing and use of packet radio without some additional tool would be very difficult, if not impossible. . . The TNC is that tool. It is connected between your terminal (or computer) and your amateur radio. Just what is it that the TAPR TNC provides? Between the interfaces to your terminal or computer and your radio is a complete microcomputer with memory and input/output devices. This microcomputer with appropriate software is used to implement the packet radio protocols. Thus any computer can be interfaced to any other computer via amateur radio using the TNC. . . The TAPR TNC connects to an RS-232-C interface, found on most terminals and home computers. A parallel interface is also provided, although not supported for terminal interfacing in the initial software release. The necessary connections exist to interface the TNC to your amateur radio equipment. These connections include lines to your external speaker (or earphone) jack and the microphone jack (both for microphone audio and for push-to-talk control). . . Also included is a complete modem used to convert the digital information coming from the computer or terminal into an analog signal (a set of audio tones) which your radio can transmit. It also performs the reverse function, converting analog signals from your receiver to digital data. Because of the bandpass characteristics of many amateur radios, an active audio filter is also included in the TNC. Passive filters proved inadequate to support transmission rates of 1200 baud - a design objective. . . Power for the electronics on the board required four different voltages: +5, -5, +12, and -12 volts. The TNC includes on board power supplies for these voltages and uses a custom wound power transformer designed specifically for TAPR and included with the board. . . But hardware is only part of the TNC. Software is equally (if not more) important, for it's the software which makes this hardware useful in handling packet radio protocols. . . The TAPR software was designed to support two interfacing requirements. The first interface is to the computer or terminal and involves processing commands and assembling data into packets. Also, packets received must be processed and formatted for display back to the computer or terminal. The second interface is the radio interface which provides two different packet communications protocols (AX.25 and the original Vancouver protocols), keying the radio, and sending proper Morse code identification using your call sign. The protocol involves accessing the shared radio channel, formatting and sending packets, receiving and deciphering packets, and filtering out packets not intended for your station. . . The software is implemented on the TAPR board in read only memories (ROM's). 24K of ROM is provided on the board for this purpose, along with 6K of on-board random access memory (RAM). . . The TAPR TNC beta test version sold for $200 - a very low price for such an incredibly well-designed and engineered unit! As mentioned earlier, the initial tests using this board have been most impressive. I'll provide a more detailed description of both the hardware and software components in forthcoming tutorial messages.