HowTo: Running the 1G Analog Phone from 1997 | by Dmitrii Eliuseev | Geek Culture | May, 2021

By SDR News On Jun 2, 2021

Analog mobile phones were popular in the 90’s and the last operators stopped their service only in 2007. Is it possible to launch this phone now? Let’s find out.

The Advanced Mobile Phone System (AMPS) standard was established by Bell Labs in 1983, and these phones became popular in the 1990s. This standard was something of a first-generation cellular technology – the voice was transmitted in the “old way” of frequency modulation (FM), as in walkie-talkie radio, but the radio spectrum was divided into separate channels and the so-called “control channel” is digital.

AMPS uses 825-845 MHz and 870-890 MHz bands, the spectrum is divided into 21 control channels and 395 traffic channels. Each client is assigned a separate channel for a single cell phone call. Some modern features were also available, such as roaming, and the process of dialing a telephone number was easy and not too different from modern telephones in the 21st century. The biggest drawback of AMPS was the analog voice transmission – any phone call could be tapped with a radio capable of tune to these frequencies, and as we know today, some journalists actually did this, trying to sniff out others. people’s secrets. On the other hand, in the 1980s, microcontrollers simply did not have enough computing power to use the secure digital channels we have today. In this way, the digital data stream is only used to establish a connection, but the voice is transmitted in an analog way, as with any other portable FM radio. By the way, even a few years ago, radio scanners made for the US market (such as Icom) had some “blocked” frequencies in the 800-900 MHz band. Of course, experts could unlock it back, but this at least complicates the task for non-specialists and makes it impossible to accidentally set up someone’s phone call.

Nowadays, not all AMPS operators obviously work, but thanks to open source and SDR technology, it is possible to manage an AMPS LAN, at least in a short range. It can be interesting not only for self-education, but also for demonstration purposes, such as a demonstration in a museum or a temporary exhibition – it’s always much more exciting when you can see things in working order than just putting them on the shelf. This is, by the way, the reason why so many museum exhibits are boring, this will always happen when things inside are not “alive” and cannot be demonstrated in real use.

Before we begin, important note: Before making any transmission, please check the local radio regulations. This article describes only the technical side, not the legal side. As a rule of common sense, nothing bad will happen when transmitting using a 50 ohm dummy load instead of an antenna, it will allow signals to be sent and received in a short range of a few meters – the telephone receiver is sensitive enough to receive a weak parasitic signal even from a fictitious load. Higher power transmission or amplifier may require an appropriate license.

Let’s start.

This is generally the easy part – searching on eBay using keywords like “AMPS brick phone” can get a lot of results, and prices start at $ 20. Delivery and tax can often be more expensive than the phone itself. The most common problem with older phones is the battery – after many years of inactivity, the battery cells can be completely dead. I would also test the possibility of calls between two phones, so I order two AMPS phones – Motorola StarTAC and Motorola TeleTAC. I chose these because the latter was cheap, and StarTAC, the protagonist of this article, just looks great. And it’s unfortunate to say, but some eBay sellers cheat. I bought this phone from eBay (seller’s name is hidden for privacy reasons):