[GreenKeys] SB-2244 and Teletype Synchronous Pulsed Transmission

[gfmurphy at earthlink.net]

Teletype's Synchronous Pulsed Transmission device enabled an external
device to control the rate at which the keyboard or the TD sent 
information to the signal line.  When a key on a synchro-pulse
equipped keyboard was depressed, the key latched, the reset bail was
tripped and a contact closed.  The transmitter clutch was held in 
the unoperated condition until an electrical pulse from an external
device operated a magnet which released the clutch.  When the clutch
operated, the transmitting cam rotated and sent the signal information
to the line. The transmitting cam also moved the reset bail to its 
unoperated position, the depressed key came up and the synchro contact
opened.  The synchro pulse contact and magnet are in series and they
are separate from the signal lines.
     Imagine a simple circuit where one synchro-pulse equipped Teletype
machine was connected to a communications device that supported the
synchro-pulse feature.  The communications device could be a 
multiplexor, modem, cryptographic device or whatever. The wiring 
is pretty straight forward: There are 2 signal wires and 2 synchro-
pulse wires. 
     Now imagine a more complicated arrangement where there are two
synchro-pulse equipped Teletype machines and two communications devices.
Let's say that machine A is normally on circuit 1 and machine B is 
normally on circuit 2. In order to move machine A to circuit 2 you
would plug a patch cord into the SET jack of circuit 1 and plug the
other end into a looping jack of circuit 2.  However, the synchro-
pulse leads of machine A are still attached to circuit 1 so you would
have to move them also.  I believe that this is the purpose of SB-2244.
It simply allows re-arrangement of the signal loop and the synchro-pulse
loop.  There must have been some patching rules because you could not
have the synchro-pulse leads of 2 machines in series.  (They would work
if they were in parallel.)  
     My thoughts on the operation of SB-2244 are somewhat speculative
since I've only seen a picture of one.  I am familiar with the SB-1203
and SB-1210.  A better understanding of SB-2244 could be achieved by
examining its wiring.  Synchro-pulse equipped keyboards could have the 
feature disabled by moving a clip into position so that the magnet was 
in the operated position.  Every synchro-pulse equipped keyboard that
I saw on every Navy Model 28 had the feature disabled.  Maybe that's 
why I never saw a SB-2244.
Regards, Jerry Murphy