Beyond Atari

by John J. Smith

 

 

Issue 17

Sep/Oct 85

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A series by John J. Smith looking at aspects of communication

Most of you know about the modem offering communication between computers via the telephone line but there is another way! The ham radio enthusiasts amongst you will have heard of this mode of transmission, it is called RADIOTELETYPE or RTTY for short. Are there any hams amongst page 6 readers?

RADIOTELETYPE

RTTY was originally developed for teleprinters but now that microcomputers are easily available noisy greasy teleprinters like the Creed 7b are being replaced so the enthusiast can come in from that cold drafty garden shed to the warmth and comfort of the living room but due to the completely different systems it is not possible to just plug in and go! The coding system used in RTTY is the Baudot or Murray system using 5 bits instead of the 7 or 8 bits used by computers in the ASCII standard. In addition the baud rate is much slower (50/75/110) due to the mechanical nature of the original equipment.

First let me explain what RTTY is - it it a method of sending and receiving messages by radio. I must make it clear that if you want to transmit or send a message you must have the appropriate transmitting licence to do so legally so this limits the field a bit but all is not lost. If you have a radio with a short wave band tune in and listen to all those bleeps like morse code sounds. Not all of those sounds are morse, some of the very fast sounding ones are in fact RTTY signals and as these are ordinary audio signals they can be recorded on an ordinary cassette recorder which can save the sounds for you to play back later.

In order to understand these signals you will need a decoder - a sort of modem - which plugs into either the earphone socket or extension speaker socket on the radio or your cassette and another lead to plug the decoder (modem) into the computer. Once you have this all you basically have to do is tune in your radio until you hear those funny bleeps whilst watching your tv monitor screen for the printed messages to appear. Be warned though, you are likely to see things like press reports covering news to and from newspapers much of which is copyrighted and any information accidentally obtained by scanning the band should not be be revealed to a third party. Some of the commercial users transmit messages in some sort of code, usually in blocks of 5 characters, and although you will see it on screen it will be meaningless. Don't think that your decoder has gone wrong, it just prints data as it is received in the same way it was sent.
There are many ham transmissions both in the U.K. & U.S.A. and to a lesser degree worldwide and several factors affect reliable reception of the signals. The performance is dependent on the type of radio receiver of course and is usually proportional to cost but there are other things like
the time of day, the weather (yes, really) and choice of frequency which will affect results.

There has been quite a lot published on this subject elsewhere so I will not go into too great a detail here but I think that many PAGE 6 readers will be surprised to learn that their computers can be used like this.

GETTING CONNECTED

If your interest has been sufficiently aroused you will by now be asking how can a decoder be obtained and what make is the best. I feel it would be out of place in a column such as this to list specific items so I suggest that you contact a specialist ham radio shop. If you want to buy one ready made you might even get one off the shelf but it may cost you in the region of 150 to 200 for a ready built unit which might also decode morse code into printed words and come complete with built in AMTOR satellite link! If you want to build a sirnpler unit yourself, many excellent designs exist and a unit will cost you from 15.00 to 50.

This sort of equipment nowadays usually has RS232c connecters so assuming that you have a suitable interface already for use with your ATARI you should be able to conned up. A printer (even a cheap one) will come in handy too.

One final thing to remember is that computers need software to enable them to know what to do with the information coming in from the radio modem just as a telephone modem does. Several programs do exist, although I don't know of any commercial packages for the Atari. The U.K. Atari Computer Owners Club have published programs for use with radio or morse or you might like to write your own.

I hope that this article has shown that there are wider uses for your Atari. I think it is important that we do not fall into the trap of looking at our hobby with blinkers on - there is more going on in computing than you think. Although this is a specialist subject everyone should be made aware of just what can be done so that people can then start to specialise in areas that interest them. This is similar to the situation 10 years ago when many people who had electronics as a hobby realised that it was possible to build a computer and get it running. The problem then was that few people knew high level languages like BASIC (which is now a run of the mill standard) and there was no sound, no colour and no graphics so what few games there were had to be question and answer type games. People persevered though and now look at what can be done. Who knows what may become of using computers on the airwaves.

Let me know via PAGE 6 how far you can stretch your imagination and what you are you using YOUR computer for, maybe something special like ROBOTS?

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