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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