HowTo: Running the 1G Analog Phone from 1997
Analog mobile phones were popular in the 90s and the last operators ended their service only in 2007. Is it possible to run this phone now? Let’s figure it out.
Advanced Mobile Phone System (AMPS) standard was created by Bell Labs in 1983, these phones became popular in the 90s. This standard was a sort of first-generation cellular technology — the voice was transmitted using the “old way” method of frequency modulation (FM), like in a walkie-talkie radio, but the radio spectrum was divided into separated channels, and the so-called “control channel” was actually digital.
The AM PS is using 825–845 MHz and 870–890 MHz frequency bands, the spectrum is divided into 21 control channel and 395 traffic channels. Each client is assigned a separate channel for a single cellular phone call. Some modern features, like roaming, were also available, and the process of dialling the phone number was easy and not too much different from modern phones in the XXI century. The biggest disadvantage of the AMPS was the analog voice transmission — every phone call can be overheard by using the radio receiver, capable to be tuned to these frequencies, and as we know nowadays, some journalists were actually doing this, trying to sniff out other people’s secrets. On the other side, in the 80s the microcontrollers just did not have enough computing power to use the secured digital channels, we have nowadays. Thus, the digital data stream was used only to establish a connection but the voice was transmitted in an analog way, like in any other portable FM radio. By the way, even several years ago, radio scanners made for the USA market (like Icom) had some “blocked” frequencies in the 800–900 MHz range. Of course, the experts could unlock it back, but it at least makes the task more complicated for non-specialists and makes it impossible occasional tuning to someone’s phone call.
Nowadays all AMPS operators are obviously out of service, but thanks to the open-source contributors and the SDR technology, it is possible to run a local AMPS network, at least on the short-range scale. It can be interesting not only for self-education but also for demo purposes, as a demonstration in the museum or temporary exhibition — it’s always much more exciting when you can see the stuff in a working condition, than just laying on the shelf. This is, by the way, the reason why so many museum expositions are boring, it will always happen when the things inside are not “alive” and cannot be demonstrated in real use.
