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Getting Started In Digital - p2 by Larry Buck, K1HEJ, NTS-STM |
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Very briefly, in 1200 baud packet transmit, the ASCII output of your computer (1), is converted to audio tones using some combination of (2) and (3), and then is sent to your transmitter (4), and out your antenna (5), using interconnect cables (6). On Receive, the signal comes in your antenna (5), to your transceiver (4), where it is converted to audio tones and fed to your TNC or interface (3), where it's converted from tones to ASCII, and is fed to your communications program (2), which then displays the text sent on your computer screen (1). The advantage of using a TNC over a digital interface, in my opinion, is that while your transceiver draws less then 100 MA on receive, and the TNC, will often run a month on a 9 V transistor battery, you home computer draws between 15 and 20 amps when run on 12 V. Most TNC's have a built in "digi-peater" program which will allow your station to act as a non-error checking relay station. Most also provide a small on-board automatic mailbox. This allows a connecting station to leave you "mail" without you running your computer. It signals you (Via a blinking LED) that you have a message. Packet can be run on any computer that has been made since the old IBM 8088's. Almost every computer you have available - including Apple can be used with a proper program. Apple programs may be a bit harder to find, but we do have folks operational at present in CT using them. There are some very popular communications programs that were shipped with early TNC's that run under DOS in every version of IBM computers. This includes a program called ProTerm. In my opinion, based on some 20 years of running packet, the best communication program if you are running anything earlier than Windows 95 on your computer is Qmodem. Recently I had occasion to get a copy of Winpack. This program will run on Windows 95 and newer platforms and does everything Qmodem does; but does it while you are in Windows. This give you access to your windows features on your computer without having to switch over to it - from DOS, as you had to when running Qmodem. Most TNC's have a built in mailbox. By leaving your TNC and transceiver on, other stations running packet can put messages into your mailbox - even if your computer is not turned on. With A digital interface your Home computer must be turned on as well as your transceiver to receive messages. Home computers - draw a lot of power. (10 or more amps at 12 V) When commercial power is on we don't care; but in ARES, where we operate when commercial power is interrupted, power consumption demands are important.. Many of us now use portable computer. They use less power. |
