Old Meets New: Analog (1G) TACS Cellphone meets Lime SDR

Thanks to the excellent work done by Andreas Eversberg on osmocom_analog I managed to revive a Cleartone CTN9000 ETACS “handportable” mobile phone from the late 1980s using a Lime SDR to emulate the old analogue radio network.

I’d recently purchased the Cleartone phone from eBay purely as a prop for a 1980s-themed birthday party but after the party I started thinking about getting it to actually do something.

The phone dates from around 1989 according to this info I found. There’s also a comprehensive teardown here.

The design of the (E)TACS system was similar to most other analogue mobile networks at the time: signalling between handset/network was achieved by tones/FSK and fwd/reverse voice channels used basic FM (remember the various scandals that came from “journalists” listening in to private calls?).

The Tx/Rx frequencies used between handset and BTS in (E)TACS were around 900MHz and those frequencies are now used for GSM/3G/LTE, so actually transmitting in the open air is illegal in the UK. All my tests were done either with a direct cable connection or in a screened room.

Both old Ni-Cd batteries supplied with my phone were beyond dead – both had oozed & leaked and very badly corroded their terminals.

After hooking up a 7.5V PSU directly to the phone’s battery terminals it sprang to life and revealed its PSTN number as "0836 257712". From the data on the osmocom analog pages it looks like this was a Vodafone UK TACS phone and so we now know the initial paging ID to feed into the software. I downloaded and compiled the software from https://gitea.osmocom.org/cellular-infrastructure/osmocom-analog/ and we’re off… luckily it comes with a “--limesdr” option that sets things up for the SDR I was using. I simply ran the command:

tacs -k 0023 -O --limesdr 0836257712

I think the phone’s electronics are on their way out – 50% of the time on powering on the phone I see a “ERROR PLL” message on the screen 😦

Despite this I’ve managed to successfully “call” the handset via the SDR a few times.

---

I thought about the possibility of integrating the analog handset into my PBX but… ( – later – ) … it looks like the handset has now permanently died – it shows “ERROR NAM” every time it’s powered on 😦 And there’s a really odd smell (“hot electronics” mixed with fishy smoke! Yeuuck 😀 )

So for now the handset’s relegated to the status of ornament on my 1990s stereo system 😐

The phone’s charging station had the spare battery left in it where it had leaked and corroded the contacts and PCB. The build date (89-07 i.e. July 1989) sticker is visible on the heatsink.

References:

https://hackaday.com/2018/11/03/revive-that-old-analog-cell-phone-with-sdr/
https://hackaday.com/2017/01/16/shmoocon-2017-dig-out-your-old-brick-phone/