The latest addition to the Tetra-to-Echolink project is a Motorola MTM800E. In this case ‘E’ stands for ‘Enhanced’. Although the front of the radio looks identical to the MTM5400, this radio is an improved version of the MTM800. On the other hands the MTM800 looks identical to the MTM800, but has some big technical improvements.
Under the hood a lot has been changed. The MTM800E has more possibilities to grab data from the PEI interface, which is the main reason to get hold of this radio. At the end SDS messages have to be read from the PEI port and will be translated into commands for SVXLink. The ‘old’ MTM800 which is currently my Echolink node transceiver has insufficient options for this. But that’s not an issue at all, because I’m going to use the ‘old’ MTM800 as my /M transceiver. Luckily this radio already has a remote mount option AND the built in GPS module. I’m already thinking to use this for APRS…
Programming the 800E and reading the PEI data wasn’t easy at the beginning. Here some quick wins to start with.
Front or backside programming?
Apparently this set can be programmed via the microphone connector at the front and the accessory connector at the backside. But I only succeeded to program the radio via the microphone socket. The home built programmer for the back side (working great for the old 800) isn’t usable. Just don’t try it, because the accessory socket of the 800E expects 3V3 and the programmer gives a TTL level of 5V! Furthermore only programming via USB seems to be successful, using RS232 cables isn’t. Nevertheless you can purchase a cable to connect the accessory connector with a COM port of the computer: this is the ‘active data cable’ to interface with the PEI port. So it’s not meant for programming.
A USB programming cable for the microphone socket can be found on a common auction website. There it’s a bit cheaper than an original Motorola part. But at the end it’s fulfilling the same job.
According to the service documentation of Big M the set will automatically kick into programming mode after connecting the USB cable and firing up the set. It will take some seconds before the radio recognizes the computer at the other end of the cable. Then the display of the radio will show a warning not to disconnect the cable. With my set this also worked like this for some time. But probably I’ve activated or deactivated some option I even can’t remember, but the radio is not going into programming mode automatically anymore. That’s not an issue at all, because the key combination  +  + power on convinces the set to go into programming mode. It’s really important to push the keys exactly as described:
- press  and keep it pressed;
- then press  and keep it pressed as well;
- while  and  are still pressed, power up the radio and release all three keys after a second.
What about the accessory connector?
Service manual, installation manual and internet message boards aren’t aligned: is it possible to grab serial data from the accessory connector using an ‘active data cable’ or not? Taking the short cut: ‘yes, that’s possible’. No additional interface boxes, enhanced control heads or whatever are needed. Pin 19 and 20 offer serial data with 3.3V TTL level. To test things out I’ve crafted a quick and dirty data cable using a 3V3 FTDI chip I had in stock. This chip is recognized by Windows flawlessly and will be managed as COMx (probably drivers have to be installed first). Using a terminal applicaiton like ‘Termite’ AT commands can be sent and received. No handshake is needed, just make sure to set the communciation parameters correctly. By means of the test I’ve used 9600N1 but the speed can be increased without any issues. Communication parameters of the radio have to be altered with CPS Plus.
And when using CPS Plus also make sure to set the correct behavior of the PEI interface:
‘Data Services‘ > ‘AT commands‘ > check all three options (‘ETSI Group Setup Format‘, ‘ETSI AT SDS/Status Format‘ and ‘Extended ETSI Addressing‘).
After setup of the serial connection testing can start by typing ‘AT’ (without quotes) in the terminal window. The set has to respond with ‘OK’. If it doesn’t, something went wrong with the settings, the wiring or both.
In case the set responds ‘OK’, SDS and GPS data aren’t piped automatically to the PEI interface. You’ll have to activate the correct service profiles:
Activate SDS pipe to PEI –> AT+CTSP=1,3,130
Activate GPS pipe to PEI –> AT+CTSP=1,3,131
Register SDS status handling –> AT+CTSP=1,2,20
Register GPS LIP hanadling –> AT+CTSP=1,3,10
From this point on you can start testing using another Tetra radio (preferably with GPS) by sending status and SDS messages. When testing with a GPS enabled radio you’ll also see position data in the terminal window.
The data in the terminal window is partially in hexadecimal format and consist of two lines. The first line contains a tag marking the type of output (in this case ‘+CTSDSR’), followed by the ISSI numbers of sender and receiver. The second line is interesting, because this contains the message body in hexadecimal format. This can look like: