[GreenKeys] AP/UP/etc "broadcast"

[Jim Cook]

On 6/21/2010 21:22, Pete Lancashire wrote:
> Any doc's on the web how AP/UP/etc "broadcast" to their 1000's of subscribers ?
>
>    

I worked in an AT&T Toll Test office in a major city
for years.  We had dozens of TTY loops on 'wet' cable
pairs and many more loops using Western Electric
43A telegraph carrier for the distribution of the wire
services.

The very interesting thing for me was the way the circuit
was 'multi-pointed'.  The receive channel keyed a 20ma
130volt loop.  The loop had resistor taps (2.2K I think)
that sent the voltage to the grid of a tube in a device
called a HUB driver.  The driver keyed the local wet cable
pair (20/60ma) or it keyed a voltage into the 43A channel
unit for transmission to the sub (by tones)..

All very interesting to a guy that worked 20ma and 60ma
loops in the Army. The concept of sensing the keyed
voltage seem novel me at the time (hey I was a kid!)<smile>

IE.... at AT&T 'we did it with LOTS of tubes!'

Some time during the mid to late 70's AT&T (and other
long haul common carriers) lost the distribution of the
wire services.  The providers moved the network over to
satellite.  AFSK continued to be used but now rode as a
sub-carrier on a network voice channel over a satellite
transponder.

--
JimC