[Qcwa] WWII RTTY

[Jeffrey D Angus]

ka2e@att.net wrote:

>My father was on Biak island (Dutch East Indies)
>
Which by the way, is as far as you can go from Hawaii on a 747 without 
having to
stop for fuel. (I stopped there several years ago on the way to Bali.) 
Interesting
"airport" There's a 4' chain link fence on either side of the runway and 
it's all
surrounded by vegetation. Walking out of an air-conditioned airliner, as you
step down the stairs, you get hit with the heat and humidity.

>(A photograph of the TTY/CRYP room is at the following URL:
>http://home.att.net/~ka2e/dad/pic54.jpg)
>
>a.  Can anyone identify the TTY gear at the right?
>
They look like Teletype(tm) Model 15 page printers. The Model 19 tape sets
took up more space width wise.

As a side note: The Model 15 ran best at 60 WPM, but due to the nature 
of the
mechanical linkage, you were limited to typing at 30 WPM (every other 
cycle.)

>b.  What type/power of transmitters/receivers would have been used?
>
A lot of dual diversity receiver setups to cope with the selective 
fading of one of the two
tones used. (As mentioned previously, FSK, two carriers 850 Hz apart)

Special transmitting equipment, due to the KEY DOWN nature of TTY 
transmitting.
A lot of stuff was done by the Technical Material Corporation.

>c.  How were the TTY machines interfaced to the transmitter/receiver?
>
A TU, or Terminal unit, converted the recovered audio tones to Mark and 
Space keying.
Either Simple make and break, or Bipolar (reversing the current in the 
loop) type keying.
For transmitting, either a single channel FSK (Frequency shift) using a 
keying relay to
add a bit of capacitance across the carrier oscillator. Or AFSK, audio 
frequency shift
keying using either two tones, or a number of tone pairs (two for each 
TTY machine)

At one time in my distant past, I had a two bay rack of AN/FCC-? 
something. That was
basically ten transmitter and ten receiver tone pairs, the combiners and 
such to put 10
TTY machines on a single radio channel.

>d.  What frequencies were used?
>
Typically, something between 6 and 12 MHz, er ah, KC. It was still 
cycles in them days.

>e.  Generally, how did the TTY machines operate? I'm told they punched a lot 
>of traffic on paper tape and sent it later.  Communication was also done 
>directly at the keyboard - how did they switch between transmit and receive?
>
The Teletype(tm) machines were a mechanical marvel to watch.

On transmit, There were 5 code bars the ran underneath the keyboard. 
With variations of
_|\_ or  _/|_ and _/\_ ridges on top, that would shift the levers either 
right or left when a key
was depressed. This in turn would make or break 5 individual 
(sequential) contacts that would
form the 5 bit Baudot serial code. One Start pulse, 5 code pulses, and 
1-1/2 stop pulses. A
forerunner of modern ASCII asynchronous data.
On receiver, the selector magnet would release a clutch cam, starting 
the sequence, then
depending on the pull in or drop out position at sequential times 
afterwards, it would set the
receive code bars to a specific position, then actuate the printer (or 
operation).

Typically, there would be three positions on a switch at the machine.
Transmit, Local and Receive. The local loop by itself  Just allowed the 
operator to
type and print what he was typing. In transmit, He would type, print 
what he was typing
and the loop would be connected to the relay in the transmitting 
equipment. On receive,
The loop would be connected to the relay in the decoder unit.

Additional comments to the Model 19 tape set:
One of the features of the Model 19, was the ability to "disengage" the 
keyboard from the
mechanical drive system of the teleprinter, and punch paper tape 
directly. Hence, you were
not limited to 30 WPM (or 1/2 the receive speed of the machine due to 
mechanical cycling.)

A transmitter-distributor was used to take the information for the 
single row of holes and
set sequential wiper contacts to either mark or space.  A form of 
parallel to serial conversion.

The "tape loop" was in effect a type ahead buffer. "first in, first out"

Other mechanisms in use were the "mite" small portable field units, and 
the Kleinschmidts
which had a rotating type mechanism, sort of a forerunner to the IBM 
golf ball approach.
Unlike the Teletype(tm) model 15 series that used a moving type basket 
much like a
regular typewriter at the time.

Ahhhhhhhh, as I've always said, "Real keyboards have green key caps."
That and the hum or rotating machinery and the smell of warm machine oil.

Jeff



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