Motorola MTM800: GPS or not?

In fact the Motorola MTM800 which is acting since a while as Echolink node transceiver is a real mobile device. It has a remote control head and the optional GPS unit has been built in. The last mentioned wasn’t built in by myself but already present when I’ve bought the set. The CPS showed me the ‘feature flag’ for the GPS had also been activated already, so the GPS was ready to use. Nevertheless I didn’t have a GPS antenna so I didn’t pay much attention to this feature.

But as the situation has changed when I’ve got an MTM800E as node transceiver, the MTM800 became an interesting option to use as a mobile Tetra transceiver for my car. And in this context also the GPS became interesting again. Because in combination with SVXLink the position data can be fed into the APRS network. Therefore I needed a GPS antenna with FME connector, which is really cheap to get via the internet. The documentation of the MTM800 taught me the set offers a 5V (20mA) phantom power supply. And that knowledge made it easy to obtain the correct antenna via the internet.

First the set was connected to the computer to enable the GPS unit and to have the GPS service option enabled in the radio’s menu. The antenna was connected and the set fired up. After some minutes the display still showed the warning message about insufficient satellite coverage. And the service menu showed exactly 0 satellites within range. This was weird because the MTH800 had already given a beep on satellite lock. Therefore I’ve decided to start checking the power at the FME connector: bingo! No 5V present at the antenna connector. So very obvious that the satellite antenna didn’t pass on any signals. The GPS unit could be faulty, but that seemed rather unusual to me. Luckily enough the GPS print is easy to access via a small ‘hatch’ at the bottom of the radio. After having this opened I could completely take out the PCB, with a nice little flat cable at the bottom side. And at the mainboard of the radio the corresponding connector with open clip was visible. So the GPS unit was present in the radio, but not connected. Or the one who had built in the GPS had forgotten to lock the connector of the flat cable. Anyway this construction was never able to work properly!

With some fiddling the cable could be put in place and locked in its socket. After putting the PCB in place and leading the antenna cable out of the radio via a rubber seal the hatch could be closed again. After powering up the radio the satellite coverage warning disappeared within one minute, and via the service menu I could see how the radio had identified 6 GPS satellites.

So the moral of this story: also in the complex Tetra world a solution can be astonishing easy!