[GreenKeys] Model 28 Telex?

[Harold Hallikainen]

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.