[GreenKeys] Model 28 Telex?

[Jeff G]

The dial of Telexes baffled me as well which is why I had to look it up.
Basically my take is that the loops, etc all evolved from telegraph, and
that Telex basically took telegraph loops and added switching to them,
hence the dial, but it wasn't POTS, in fact a completely separate signaling
system with different phone numbers. Signaling is done via loop control,
for example reversing polarity tells the CCU the call is connected, etc.
This is how we get 32s to work; just flip the polarity on the loop and the
CCU thinks its call connected and works like a normal TTY. I think TWX was
the evolution of Telex where it was a simliar system except using modems,
ASCII, and standard voice/POTS lines. I know there was some computer
integration between the two as well for a bit as I had some WU materials
mentioning that.

Jeff



On Tue, Jun 24, 2025 at 2:21 PM Harold Hallikainen via GreenKeys <
greenkeys at mailman.qth.net> wrote:

>
>
> On Tue, June 24, 2025 11:08 am, R Russell Miller wrote:
> > Jim,
> >
> >
> > You are correct!
> >
> >
> > A Western Union Telegraph Company Telex machine interfaced with the Telex
> >  exchange in one of two ways.  The first option was a "local loop" which
> > was a 5 ms loop when the Telex machine was idle and then a 60 ma loop
> when
> > the Telex machine was in operation. The second option, sometimes called
> > long distance or polar was used when a 60 milliampere connection could
> not
> > be achieved, provided a ground return polar circuit using 35 milliamperes
> > on separate send and receive wires.
> >
> > 73
> > Russ WA3FRP
>
> Interesting! I may be confusing various message threads. Was this a
> machine with a telephone dial on it? That made me think it operated over a
> POTS voice circuit. On the above described DC circuits, was pulse dialing
> used? How?
>
> The feed of one wire against ground is interesting. So much for balanced
> lines! I suspect this caused some pulse crosstalk into other pairs in the
> cable.
>
> Back when I first started working in radio, we had a Gates RDC-10 remote
> transmitter control (
> https://bh.hallikainen.org/uploads/harold/Gatesrdc10c.pdf ). For control,
> it used various voltages and polarities on tip or ring to ground. A second
> DC pair carried the metering sample. We soon replaced this with a Moseley
> TRC-15A ( https://bh.hallikainen.org/uploads/MoseleyTrc15a.pdf ) that used
> frequency shift keying for the control. It would shift the tone frequency
> for varying lengths of time for different functions. Metering used a
> voltage controlled oscillator.
>
> At the same station, we had a model 15 wire service machine with a tone
> demodulator (Lenkurt, I think?).
>
> --
> Not sent from an iPhone.
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