The Computer In Radio Communications
                 By
                 Marilyn Hartley KJ 4 GV

    Come with me please and let's take a ride in my time machine.  We won't goback very far, maybe 60 or 70 years.  The first thing I want us all to see isthe teletype.  The original teletype was the stock ticker which operates on
the same principle as the teletype.  I'm sure that you have seen a teletype in some movies.  They are generally big, black, dirty, and most of all, very,
very, noisy.  Basically, all the teletype in the 1920's and early '30's is
nothing more than a fancy typewriter with an electric motor and the circuits
to communicate with another teletype by a dedicated telephone line.  This is
accomplished by sending an electrical signal down the phone line broken into 5bit signal characters.  This breaking of the signal is called "mark and space"or "on and off.  

    Well, let's move back to the time machine and go forward to the early
1940's and what we now know as World War II.  The computer as we know it todayis only now taking form.  IBM built the first computer and called it the Mark I.  Here we see the Mark I at Harvard University in its glassed in, air
conditioned room.  This computer was constructed using tubes and was a
monster.  It only had 3,304 relays and was used for 16 years.  Now the Mark I
is in a museum.  Our next stop will be a very short one at the Bell Labs wherewe watch the invention of the transistor.  Must move on, so let's go forwardto the 80's and the desk top computer era.  

    Now we have a personal computer that is very small and will do more,
faster than the IBM Mark I.  With the use of an interface, I can use the
computer to generate a number of codes and languages for use with a radio. 
Now "mark and space" is a set of tone frequencies separated by a distance
measured in cycles per second.  This is called the shift.  Narrow shift is 170 cps, while the wide shift is 850 cps.

    The computer mates to the interface by cables and is program driven either by plug-in cartridge or from software on a disk.  The interface takes keyboard information and then sends it to the radio in the proper format.

    For Radio Teletype or RTTY,  the interface connects to the radio by way of the microphone input and the speaker output.  The interface on transmit
generates the tones of the proper frequency and shift and the radio then
transmits these tones.  The reverse happens on receive.  The radio receives
the tones and they are sent to the interface which translates the rtty signals to the language of the computer.  The computer now displays the message that was received as rtty tones.  The same process occurs for Packet, which is a method allowing for better than 95% message accuracy at the receiving station. Other modes of operation include AMTOR (AMateur Teleprinter On Radio) and CW.  CW stands for continuous wave and is a fancy name for the international form of Morse Code.

    This all sounds very complicated, but it isn't.  The computer is the tool
that today makes landline teletype or rtty much simpler.  In fact, if it were
not for the computer, the teletype of even the late '60'S and '70's would have been much larger and noiser than they were.  Thanks to the computer, today's teletype can be of a size not much larger than a desk top computer and printer combination.