We think of the cell phone – well, what we would call a cell phone – as something quite modern. Many of us still remember that using an ham radio patch from your parked car would have made people stare and whisper. But it turns out that in the late 1940s, Bell Telephone was offering mobile phone service (MTS). It was expensive and didn’t work as well as what we have now, but it did allow you to make or receive calls from your automobile. After the break you can see a promotional film on MTS.
The service was deployed to St. Louis in mid-1946. The 80-pound radios went into the trunk with a remote wired to the dashboard. At first there were only 3 channels, but later Bell added 29 more to meet demand. An operator connected the incoming and outgoing calls and if three other people were using their cell phones, you were out of luck.
Use cases and equipment
The video shows a team of truck drivers receiving a call for an unscheduled pickup, then a worker calling the main office while in the field. There were a lot of manual steps in determining which base station to use for the call. It’s not obvious until the end of the video, but the system was half-duplex. You had to press a button on the handset to speak.
The radio equipment appears for about seven minutes. Be ready. They will tell you that both units are “compact!” ” The dynamo that supplies plate tension to the transmission tubes is probably 15 times the weight of your biggest cell phone. Not to mention that your vehicle might need a larger battery and alternator. As big as they were, the power output was only around 3 watts.
If you want more technical details and nice photos, [wb6nvh] has a very good page detailing the history of MTS.
Around the eight minute mark, you can see the base station’s antennas and radios. In the middle was an operator seated at a conventional switchboard. There were two services available: an urban service which had radios in towns and the road service had antennas along major roads.
The frequency, by the way, was in several bands. The low VHF band was around 40 MHz for motorway service and around 150 MHz – not far from the current 2 meter amateur band – for urban service. At first you had to listen to the operator to announce your cell phone number, but this was quickly replaced by selective calling as seen in the video.
There was a variant of MTS that used shortwave frequencies and a single sideband. Of course, it was loud and temperamental. There was also some use of MTS to make public telephone calls in a train.
Before the cell
Common sense would suggest that a “good” radio system would have high power and a large footprint. The problem with this is that the larger zone invalidates a channel for all users in that zone.
The key to the success of the mobile service was to make the transmitters weak and the antennas very directional and short range. This allows you to restrict a set of channels to a small region or cell. These same frequencies can then be reused in a neighboring cell, but not adjacent to it.
This made it difficult to integrate too many customers into the mobile system. In some cities, the waiting list was around three years. The prices were high because the systems were often at full capacity, so encouraging new subscribers didn’t make sense.
MTS dragged on into the 1980s. But by 1964, the writing was on the wall and Enhanced Mobile Phone Service (IMTS) was available. IMTS has direct dialing and full duplex. A common IMTS phone, the 25-watt Motorola TLD-1100, had two approximately 8-inch square circuit boards for locating an inactive channel and handling other channels via audio tones. That is, an inactive channel had a transmitted 2 kHz tone, while a busy channel had 1.8 kHz. You can even put an IMTS phone in a carrying case.