car phone

Like two way radios, though perhaps some were duplex (I know some two way radios were designed for duplex, but never saw why).

There were a handful of dedicated channels per a given region. A central tower, and an operator at that central tower. You'd call up the operator, give them information and they'd dial. I think they dialed. The person you want to talk to would answer, and you'd have your conversation. There must have been tone signalling so someone could phone you in your car, a specific set of tones causing your car phone to "ring".

It was very expensive. Big radios for much of the period that sat in your trunk, I suspect they were rented but maybe one could buy. That would be connected to a tiny box under the dashboard of the car, which had the needed controls (very minimal) connected with an often thick cable (because various lines had to run). And since there were only a few channels available, there had to be a high charge, to pay for the infrastructure spread only over a relative few who could afford it, and to ensure nobody hogged the channels.

Most people couldn't afford them, and it couldn't be for the masses since "bandwidth" was rapidly filled.

Cellphones fixed the problems. First, they got more channels allocated, albeit at a higher frequency. That allowed for more users. But by keeping signals weak, and multiple "cells" each frequency could be reused once out of a small geographic area. (With one central tower as used by car phones, since they had to have range for the full area, somebody on the other side of town could not use that channel at the same time.) If the range of each cellphone tower was about five blocks, for instance, then a few blocks away the same channel could be reused. It's a lot more complicated system, since each cell used a set of channels, move to the next cell and a different set of channels were used, and they'd be switched automatically as you moved. The fact that by the time cellphones came along computers could be put in each phone helped a lot.

By adding a lot of infrastructure, all those cell towers, it allowed for a lot more users. Taht dropped costs, which in turn meant more people could afford it. Since it became a mass market item, rather than hand built transceivers, production costs went down, making things cheaper again. Once there was enough users, they could leverage more channels, and then eventually go to even more efficient methods of using the frequencies, allowing for even more users.

Michael

Yup, mostly Motorola and GE, and an adaptation of the gear used for police and taxicab service. Later ones had touchtone pads for self-dialing. The car phone had a tone ID when beginning a call for billing purposes. The units in the trunk were roughly 16 x 16 x 5" or so.

Jon

Telephone users aren't used to saying "Over".

Yes, probably they were duplex. I never used one, obviously. I recall instances of people being warned about how to talk over the radio, but that was likely on the Marine band where I thought there was some sort of phone patching going on, or more obviously on 2m fm with an autopatch.

The problem with duplex was not only that the power supply (all those vibrator supplies) had to power both the receiver and transmitter at the same time, but keeping both in use at the same time meant lots of effort had to be done to keep the local transmitter out of the receiver.

Michael

Yes, I still have some of that junk in the basement, surplus forty years ago. The cases alone were heavy by themselves.

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I have been told, that only one (or a few) could use it at a time as all phone were on the same frequency. Therefore everyone could listen to the phone calls.

I wonder how they contacted the car.

There is this story - that a guy phones his wife, that he will be late, then his mistress - for everyone to listen to

Sonnich

(Context: Assuming IMTS service from late 60s through early 80s)

Depends on the locality -- there were about a dozen channels available in each of two bands (one around 150 MHz and another around 450). All the tech details you could want are in the Wikipedia article:

In any one "system" (i.e. metro area) one of the available channels would transmit a continuous "idle tone" and all receivers would scan to that channel. Signalling came from the tower - all mobile sets would listen to the signalling spill for their own Mobile ID. As soon as your mobile knew it wasn't being signalled it would pick up scanning. If there were NO idle channel, it would typically illuminate an "all channels busy" lamp.

Everyone who worked in the industry has a story like that - it happened often enough that it was a common occurance. Or something equally devious.

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It was a small number of channels, and yes, only one person could use a=20 channel at a time.

One method comes to mind, which was used somewhere and probably was used=20 here. A very low frequency tone, low enough so it could be filtered out without affecting the speaking. A distinct tone for each unit, and the=20 receiver wouldn't output audio unless the tone for your unit was being=20 sent. So all receivers were listening, but the user could only hear=20 something if their tone was being sent.

The interesting thing is that it did ensure that others with car phones=20 could not hear someone else's conversation, it would never get to the=20 handset even though the receiver was listening to the channel.

But it did nothing to protect those just listening with a receiver on that= =20 frequency, they'd hear all the transmisions. The protection was somewhat= =20 of an illusion, since it didn't prevent people from listening in, just=20 made the system look like it was dead until a call for you came along.

I gather FRS walkie talkies use something like this, tone encoders and decoders so you only hear what's being sent along with the selected tone. It seems like nobody else is out there, but turn off the tone system and=20 you'd hear anyone on that frequency.

Just everyone listening in at home.

The "protection" was that initially few had receivers for the frequencies,= =20 which of course changed as the sixties progressed and "Public service=20 band" receivers which covered those frequencies became more and more=20 common.

Michael

And a lot of the cell phone antennae around here aren't mounted on towers but hung on buildings instead.

No, they were audible tones. They had a burst of 3 - 5 tones at the beginning of a connection, to activate only the required receiver. It was called selective calling, and if you look up "plectron" Google or Wikipedia has lots on those systems. They were also used to selectively call police cars, cabs and fire trucks from central dispatchers. The original devices used tuned reeds (essentially tuning forks) to detect the frequencies. That was back in the 60's when the tranceivers were all-tube.

Jon

and there's this one.

two (known) people made recordings, how many more were listening?

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?? 100% natural

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What is more interesting about cellular technology is that it was in fact a Bell Labs innovation. It originally was thought about in the

1940's but technology had to catch up and in the 70's they started doing trials in the Illinois area.