[GreenKeys] I bought one like this on ebay

[Bruce Gentry]

I worked on mobile phones in the 1970s, the selector was still used. 
Almost all that I worked on were General Electric Progress Line with 
beefed up power supplies and cooling fans to allow full duplex 
operation. They also had duplexing filters added so one antenna could 
serve. I left that craft in 1978, but a friend had one of the systems in 
his car until 1982. I have no idea when they were finally taken off the 
air. If you were a ham, there were lots of autopatch repeaters around, 
but your conversations had to comply with amatuer radio regulations.

     Bruce Gentry, KA2IVY

On 2/22/22 22:56, Jim Haynes wrote:
> 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
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