[GreenKeys] I bought one like this on ebay

[Jim Haynes]

Well from my memories of the Highway Mobile Radio Telephone Service,
which operated in the 35-50 MHz band, the original radios were Motorola.
The installation was separate boxes for receiver, transmitter and the
selector thing.  Later used radios by G.E. that had the transmitter
and receiver in the same box.  That change might have happened when
car power systems went from 6V to 12V.

To call a mobile unit from an ordinary phone you had to ask for the
mobile service operator, same as if you were making a long distance
call.  The mobile service operator had a dial on the switchboard
and connected to the control terminal in the central office.  The
wheel in the 60-type selector is advanced by current reversals rather
than by current pulses.  So the dial digits were put through a relay
circuit that was a binary divider, changing from one state to the
other on each dial pulse.  The dial signals were sent by FSK, 600
and 1500 Hz.  The phone numbers for the mobiles were like ZFd-dddd
so they looked like ordinary phone numbers.  However the second
letter was A through F and indicated  the pair of transmitter and
receiver frequencies.  These were assigned geographically.  Most
mobile units were set up for only one frequency pair, but I once
saw one that had a rotary switch that could be set to any of the
frequencies ZA through ZF, this being for mobiles that might travel
throughout the U.S.

The mobile units did not have dials.  The user would operate the
push-to-talk button on the handset and the mobile service operator
would answer.  Then the mobile user gave the landline number to
the operator and got connected just as if it were an incoming toll
call.

The radio system was set up as a repeater, with several receivers
spread over an area but only one transmitter.  (more powerful transmitter
than in the mobile units.  There was also a test transmitter at the
control terminal operating on the car transmitter frequency that could
activate all the receivers and allow measuring their performance.  The
control terminal would select from the remote receiver with the strongest
signal.

This is the only mobile system I had any experience with.  I know there
were later ones ultimately leading to the cellular systems we have today.

 	---

 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man