Jonathan writes "With the recent influx of technician class operators, over commercialization of the Internet, and continued public interest in computers, now may be a great time to renew your fascination with packet, or create your own new digital packet radio network without spending a dime (or at least under $5). The trick is to use your Personal Computer and sound card to emulate the functions of a Terminal Node Controller-- A device that acts like a typical dial-up modem for the radio (although a TNC has considerably more complexity). In fact, the software that provides the TNC functionality, AX.25 and Sound Modem, is considerably more advanced and feature packed than even the best commercially available software for any operating system and high priced TNC. With the simply amazing tool, Sound Modem, one can create a Terminal Node Controller, such as a super high-speed 19.6 kbps frequency shift keying TNC, all the way down to a simple 1200-baud audio FSK modem. In order to accomplish this, all that is needed is a PC with a sound card and the Linux operating system, a 6-meter or higher frequency radio, and a couple simple electronic devices (which can be built for under $5 in less than an hour). The first step in setting up your new free TNC is to install the Linux operating system on a PC. If you are not familiar with Linux, you can learn more at http://www.linuxhelp.net. After you install Linux, you must next install the various AX.25 utilities that allow Linux to interface with a TNC. These can be obtained from your Linux distribution (they are not usually installed as standard equipment, and include ax25-tools, ax25lib, etc.), or from www.rpmfind.net. Next, you must acquire a compatible sound card. These include Crystal chipset cards (old and hard to find), the older Sound Blaster cards (easy to find), and Windows Sound System cards. Now days, nearly all sound cards are Windows Sound System Compatible. Keep in mind, however, that most of these so-called WSS compatible cards actually require special software to do the job. It is for this reason that I highly recommend you pickup an old Sound Blaster 16 ISA (non-Plug n Play) to keep from frustrating yourself. The next step is to build the simple, yet necessary, hardware to interface your computer with your radio of choice. The three computer input and output “ports” that will be used on your computer are your sound card’s microphone jack, the audio out jack, and your serial port. The mic jack on the sound card is used so the computer can decode the analog signal from the radio’s audio out jack, while the audio out jack on the sound card is used to transmit into the radio’s microphone input. Since all radios have a Push to Talk button (you could use VOX, but its not recommended for speed reasons), your computer also needs some way of putting your radio in transmit mode. For most radios, this means a little one-transistor-project that hooks from your PTT line on your radio to the DTR or RTD pin on your serial port. If all of this sounds confusing, don’t worry; you can obtain all the necessary schematics from this site: http://www.deskmedia. com/~jjeffers/packet/soundmodem/ptt.html Finally, after you have connected your sound card and serial port to your radio, you must now setup and configure the AX.25 protocol for Linux. This is a complex process. I can tell you that it took me many hours and several days to get the entire project working properly. However, most of this time was wasted fooling around with sound cards and the PTT circuitry. Hopefully, the above tips will make those operations short and simple. On the other hand, the first step in configuring AX.25 and Sound Modem for Linux is to recompile the Linux kernel with all of the AX.25 and Sound Modem options enables as “modules”. Then, you must load these “modules” and give the Sound Modem driver the proper instructions for your sound card. Finally, you must setup two small configuration files (/etc/axports & /etc/ax25d). Then, you must load the port you created using “ifconfig”, and then run “ax25d” and “mheardd”. If all this sounds like Greek, don’t worry, that’s normal. All you must do is visit http://www.linuxhelp.net/LDP/HO WTO/AX25-HOWTO.html, for a comprehensive, but slightly confusing walk through of the process. Hopefully I haven’t scared you away by now, but if you are still with me, you fill find that this solution is a very practical, space conscious, thrifty, high performance, and advanced way of using packet radio. Again, the tools provided with Linux for packet radio are simply outstanding. With Linux, a packet modem literally becomes, to Linux, a seamless connection to the world. You can use it just as easily as you would any other type of connection, such as dialup, a home network, or a LAN (subject to legal restrictions, of course). If you have any burning configuration questions, which you cannot resolve, you may e-mail the creator at terry@perf.no.itg.telstra.com.au. Or, you may e-mail me at jacox@home.com. 73 and happy packetering, KG6AZK."
