[GreenKeys] TGC-1

Wed Jul 25 22:38:31 EDT 2018

Nick, Chuck and Group:

Someone asked about AN/TGC-1 teletype gear, so here is some background
information on how this equipment was used and how it worked.

Look up ACP-127 online. The title is Tape Relay Instructions. It explains
more in detail how tape relay messages were constructed. ACP-127 was
common to all US miltary and most NATO military teletype networks, since,
at the time, tape relay systems were DoDs worldwide backbone messaging
system. ACP stands for Allied Communications Publication, and was common
to all NATO countries who used the same formats, and many of these NATO
teletype networks were Gatewayed into US systems. ACP-121 and ACP-122
for network architectures for those eras. Very well thought out back then.

Regarding the number sequencing process for the AN/TGC-1 tape relay set.....

As I recall, the AN/TGC-1 had three (3) TDs (or TD heads).

The far left TD was where the Channel Numbering tape was placed. This was
usually a pre-prepared tape containing the numbers 001 thru 000 (or 100) for
the 1940s and early 1950s tape relay eras, before the advent of the Plan 52,
54 and Plan 55 and AN.FGC-30s automatic tape relay systems.

Operation:

A reel of pre-prepared tape as placed in the left TD. Its job was to sequentially
number EACH message that was sent from the 2nd and 3rd TD. EACH TD
was connected to the same circuit (channel, teletype line). Only one TD could run
at a time.

An operator had to manually start a TD in order for the message(s) to be
transmitted. Prior to sending a message, it was necessary to press the button
on the top of each TD once. Usually, the Channel Numbering button was
pressed first and then a Channel Sequence Number was transmitted over
that channel. Once that number had been sent, the 2nd or 3rd TD button
was pressed which then transmitted the message.

Note 1: the Channel Numbering TD was set to only recognize or send 6 digits,
and the it stopped automatically. So, it send the Channel ID (3 letters, followed
by the Channel Number (3 numerics). If there were other characters to be sent,
such as ZCZC, they were included in the programming of that TD.

Note 2: Tape relay operators who "worked the floor" roamed from one AN/TGC-1
to another, sending (pushing) and receiving (pulling) tape. Their official title and 
duty assignment was "Expediter", but they were often called "tape apes". Many 
tapes apes were often knee deep in tape and often ran around the floor with
several messages in tape form around thier necks moving from one circuit
(AN/TGC-1) to another. They both sent and received traffic. Tape relays were very busy
places (I know -- I worked in enough of them over the years).

Note 3: As the AN/TGC-1 had both sending and receiving equipment in the same
console, they were awkward to work with, but as they were also first generation
prototypes, things changed in later years and separate sending and receiving
units were produced and arranged in relays accordingly. Thus, in later years,
you had transmit and receive operators, all still "Expediters".

Each transmitted message contained a unique Channel Number, also called
a Channel Sequence Number. The Channel Numbers were strictly for message
accountablity between the sending and receiving ends of the line. If a Channel
Number was missing (called an "Open" number), you knew that a message
might possibly have been lost somewhere in the process, and then it had to be
"reprotected", or accounted for, and resent at the next opportunity. The Operating
Signal for an Open Channel Number was "ZFX". (ACP-131 ( )).

ZFX:

OO RUFMAZ
DE RUFM
ZNR UUUUU
BT 
UNCLAS SVC ZFX AZA045
BT

NNNN

Sometimes, two messages might have been sent under the same Channel
Number. This was usually operator error, and again, a Service Message(s)
were exchanged between stations to account for both (or more) messages
sent under the same number. The Operating Signal for this error was ZFQ.

Ex:

OO RUFMAZ
DE RUFM
ZNR UUUUU
BT
UNCLAS SVC AZA022 ZFQ
BT

NNNN

Once ZFX or ZFQ messages were accounted for, no further action was required
by either station. Message Number Sheets (logs) annotated accordingly, and the
case was closed.

Accounting for message traffic in a tape relay station was usually a Supervisory
job for the "Trick Chief" (Shift Supv). He made hourly checks on each circuit to
annotate and initial that each and every channel number was accounted for.

Likewise, Channel Checks were sent manually between relay and tribs, again
to insure (a) that the circuit (line) was still operating, (b) that all equipment at
both ends was still functioning correctly (integrity), and (c) to insure that all
channel numbers sent and received agreed (accountability).

In older tape relays, at 2400Z, "FINALS" were often sent between both ends of
the circuit and on all circuits. This was a final number comparison for the RADAY.
A RADAY was the "Radio Day", which began at 0001Z and ended at 2400Z each
day. Finals looked something like this:

VZCZCFMA056
PP RUFMAZ
DE RUFM
ZNR UUUUU
BT
UNCLAS SVC FINALS FOR RADAY 365
ZIC FMA056
ZID FMA045
BT

NNNN

ZIC means number of messages SENT. ZID means number of messages RECEIVED.

Again, in older tape relays, the numbering sequence of Channel Numbers usually
started over at 001 and lasted until the last message was sent for that day. It was
possible that in high volume stations, more than 100 messages were sent or
received, the so the numbering reels would be rewound and the numbers used 
over again, but to the next hundred. For instance, 001 might be logged as 101,
002 as 202, etc. Message Number Sheets were often pre-printed with spaces
for Channel Numbers up to 100. Additional log sheets were always available if
more Channel Numbers were used.

Channel Number Formulation:

Channel Numbers usually consisted of 3 letters and 3 figures. The letters were
usually the last 3 letters (or some variation of) the stations ROUTING INDICATOR
(sort of like a Call Sign, but all letters), and then the sequential Channel Number
which followed. Ex: 

Station is RUFMAZ
RUFMAZ is a tributary station connected to (Major) tape relay station RUFM.
Channel Number serial going to RUFM would be AZA (last two letters, plus A for a single channel)
If RUFMAZ had a second circuit to RUFM its Channel serial would be AZB
So, AZA001, AZA002, AZA003

RUFM sending to RUFMAZ would use FMA (RUFM, with a single circuit to RUFMAZ.
Channel serial would be FMA001, FMA002, FMA003.

Now, to complicate things a bit, Western Union came up with a way to START and STOP
the TDs automatically in the early 1940s and this feature was built-in (early programming)
to the AN/TGC-1s and later models of both Teletype Corp and Kleinschmidt teletype
tape relay equipment.

It was ZCZC. This is called a "Start of Message" Indicator. Mostly this was used by
tape relay stations sending to their tribs or other tape relay stations. The ZCZC was a
sequential "trigger" that this was the begining of a message to be received. It actuated
receiving equipment which was programmed to recognize the "ZCZC" letters.

ZCZC was followed by the Channel Sequence Numbers (no spaces), thus
ZCZCFMA001 from the relay to the trib station.

Trips did not have this semi-automatic receiving capabilty. In those days, they were
using Model 15s and Model 19 teletype gear which were contemporaries of the AN/TGC-1s.

Instead, they used a manual Start of Message Indicator of "VV   AZA001" (VV 3 spaces, AZA001).

In later years, the VV and 3 spaces were often dropped (operator laziness) and just the
Channel Sequence Numbers were sent, i.e. AZA001, AZA002, etc

To complicate things even more, in later years, the Kleinschmidt Labs added an Upper Case
"H" as a motor stop function on thier printers. This was to save wear and tear on the machines
during longs periods where there was no traffic and the printers were just idling. Other non-
Kleinschmidt machines had a similar function, called a Line-Break.

So, in order to turn on the receiving ends printers, a letter or signal had to be sent before
the message could be sent in order to avoid garbled text being received. In essence, this
turned the line "back on", or woke up the teletype equipment which was in "sleep mode".

The "V" was selected as as the "line break" signal to activate the distant ends printers.

Thus: VZCZCFMA001, VZCZCFMA002, VZCZCFMA003. This was the "Channel Serial".....
consisting of SOM (Start of Message Indicator, Channel ID, and Channel Number).

It is likely the "V" may or may not have appeared on the AN/TGC-1 as an operator-controlled
function. Simply pressing the Channel Number button on the far left TD would have 
accomplished the line break function and then the Channel Number and Message would
have followed.

Note 4: In the early days of teletype systems, there was NO printing on tape. So, operators
had to learn to read the punch holes in the tape and got quite proficient at it. As with Morse
Code, it had to be learned and took most ops about 2 days or so to learn to look for
certain punches, i.e. spaces, CR, LF, 4 NNNNs, etc. Tape relays always had a large board on the
wall that clearly pictured all the punch holes for quick view and these boards could be
seen for several feet from anywhere on the relay floor. As a consequence, mis-sents
were not common. We were good at it! (I still am.....(smiling)......) 

Note 5: Western Union came up with the 4 NNNN to end each message. This was a
semi-automatic function that then stopped a TD from sending once it read the 4 N's.
Operators also learned to look for the 4 N's punch holes, so they knew exactly where
to tear the tape off of the machine. The 4Ns' were usually followed by 12 LTRS keys
which provided further guidance to the ops (and insured that the messages to follow
were in lower case).

Note 6: Military messages in tape form ALWAYS began with a series of "opening
machine functions" to insure that the receiving stations printer was aligned to
receive the message, and that all messages were uniform in appearance and
format. The opening machine function were 5 spaces, 2 CR, and 1 LF and then
the message header, text, etc followed.

Ex:

VZCZCFMA002    (The Channel Serial could appear anywhere at the top of each
message, but often was pre-aligned as below, unless Channel Numbers from other
stations were attached, as often was the case......(left overs thru the relay process).

VZCZCFMA002VV   AEA123
5 spaces, 2 CR, 1 LF
PP RUFMAZ
DE RUFMAL 001 1652499
ETC, ETC

Note 7: While all of this sounds complicated, it really wasn't. A trained monkey could
do this and it took a few weeks to learn it in Signal School. In the US Army, the Comm-
Center School was about about 3 months long back in the 60s and you learned everything
about how a CommCenter worked, all of its functions, references, equipment,
etc. 

The question was: Who made up the number(s) for the Channel Numbering reels?

Anyone in the Communications Center (CommCenter). 

Normally, this would have been a function of the Methods and Results (M&R) people:
the CommCenters records keepers, auditors, paper pushers, non-communicators....
and every CommCenter at the time had a M&R Section, whether a relay or a trib.
The M&R Section kept the ACPs posted and up to date (Routing Indicator Books),
bulletins, policies, procedures, checked all the logs daily, kept all the monitor reels
of transmitted message traffic, did tracers for lost or missing messages, and all
of the administrative duties incidental to an efficient operation.

At other times, the Shift Supv could/would duplicate a numbering tape, since in a relay,
they were all the same anyway. With 100 numbers on a numbering reel, at 60 wpm,
this went pretty quickly, and the numbering reels were not huge. The reels were only
duplicated when they were worn out, torn, broken, etc, and the job of duplicating one
could be delegated to any Expediter (tape ape, tape pusher = i.e. tape relay operator.

FWIW, the AN/TGC-1s came out in about 1942 first for the US Navy and later, the
US Army (and Army Air Force), and they lasted in the US Army until the mid-1960s
in some units, having been replaced by AN/FGC-35s, then AN/FGC-38s, and
finally Kleinschmidt AN/TGC-5s and AN/FGC-70s for torn tape relay, and AN/FGC-30s
for automatic relays (Kleinschmidt variant of the Plan 55 system by Teletype Corp).

All tape relay equipment could work on single-channel circuits (point to point) or
they could be adapted to wide-area HF radio teletype, such as Navy Fleet Broadcasts
or Army General Broadcasts and were used by the old Army Air Force "Airways" system.

Hope this helps. If questions, feel free to ask.....

Dave
DE RUMLNHA
Old tape relay guy

-----Original Message-----
From: Nick England <navy.radio at gmail.com>
To: David F <NNN7DXB at aol.com>
Sent: Wed, Jul 25, 2018 12:24 pm
Subject: Fwd: TGC-1

Hi Dave - 

I figured you'd be the man for TGC-1 info
best regards,
Nick

---------- Forwarded message ----------
From: Chuck <j-mcclurg at sbcglobal.net>
Date: Fri, Jul 20, 2018 at 6:50 PM
Subject: TGC-1
To: Nick England <navy.radio at gmail.com>

Nick:

I was down at Bobs, K6OSM, house last week helping him go through some of his "stuff"!  He showed me the TGC-1 and I have a question for you................Does anyone know what the Format was for the Number Tape?  As it had to change for each message I wonder how they were made up and how the machine know to only send one Header for each message.  Also, WHO made up the Number Tape?  Must have been a LOT of typing if it was done manualy......................Note to self.........Don't annoy the CPO of the Watch!!!

They must have used the NNNN sequence at the end of each message to START the header but what stopped the "number tape" and allowed the message to run???

We are up to 170 Line Items so far and have NOT started on the Shack or the Garage !!!!!

Chuck McClurg
N7UVZ
Carson City, NV
USASA 1961-1993

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