[GreenKeys] Polar Relays II

[Jim Haynes]

On Sat, 13 Jul 2024, Harold Hallikainen via GreenKeys wrote:
> Teletype got really complex to allow for all the options. Basic operation
> would require just 6 wires (2 each for motor, keyboard, and selector

Or, if you follow Irv Hoff's dictum, just 2 wires for the selector and
keyboard in series.

> You mention the use of gas discharge tubes in some equipment. I remember
> seeing NE-2 lamps in some terminal units. For example, the terminal units
> on page 299 of the 1966 Amateur Handbook has a couple NE-2s that provide
> hysteresis in the circuit.

Yeah, we made a lot of use of little neon lamps for hysteresis and
sometimes just for dropping voltage by a fixed amount without attenuating
the signal.

The ones in the FGC-5 were much larger,  in fact they looked a lot like
VR tubes except for being cylindrical rather than "tube shaped".  But
I guess the voltage drop was a lot less than a VR tube provided.

>
> To me, the most practical use of the polar relay is to interface a polar
> telegraph circuit to the selector magnets in a machine.

Yes, or for making up things like duplex sets or repeaters.  Lots of
circuits in the Long Lines green book about various operating circuits.
But all that is the stuff of telegraph transmission, not of running a
RTTY station.  And a lot of that went away when DC operation of TTY
signals was replaced by things like tone modulated carrier channels.

>
> Thanks for all the great history!
Glad you enjoy it.

In the telephone system, particularly in the days of open wire lines,
there was some use of composite sets.  A composite set is a set of high
pass and low pass filters applied to a pair of wires.  The high pass
portion is used for voice and the low pass provides for two DC telegraph
circuits with ground return.  The telegraph circuits can be duplexed so
they actually serve as four telegraph circuits, two in each direction
of transmission.

Since the voice portion of the setup won't pass the usual 20 Hz ringing 
signals there were things called composite ringers that sent and received 
135 Hz ringing and translated it to 20 Hz for the switchboard.  And later 
there was 1 KHz ringing for the same reason.  I remember being in the old
manual telephone office in my home town and hearing the composite ringers
working: click-click-buzzzz.  Which says there must have been some
composited telegraph circuits in that office, but I don't know who the
customers were.  Probably the newspapers and the press wire services.