MA-ASIG Accessory boards revisited

Rob Brookes' Blog - MRMap and Communications Info

MA-ASIG Accessory boards revisited

Postby Rob_Brookes » Wed Apr 28, 2010 10:33 am

The attached file titled "The dual control head or control head and MRMap computer, configuration for the MA-ASIG accessory board" "A9k-465_ASIG_Board_Dual_CU_V_1_2.pdf" is now available from the downloads section of the site.


For those who don't yet know, there's a wealth of information on the TMC website at http://www.tmcradio.com which is provided free of charge in order to explain some of the facilities and functions of the SRP and SRM range of Simoco radios. One of the things that comes up quite often is fitting an accessory board to the base radio to allow it to receive GPS from portables out in the field.

The reason why you have to fit the board in the first place is because the standard SRM9030 only has a single RJ45 port for external devices and this is where the control head is plugged in and so unless you unplug the control head and swap the lead for one going to your computer, you can have a radio connected to a control head or one connected to a computer but you can't have both. ** See footnote

The most reliable suggestion for extracting GPS from an SRM is to use a Dmap accessory board. In fact these have two additional ports only one of which is required in the basic 'GPS Base Radio'. If you need it, the other port can be used for a second control head mounted in a second radio operator's position or elsewhere in a vehicle for example. Unfortunately you have to use two of the same type of control head if you do this, you can't mix and match types.

Ideally, plug your control head into one of the pair of ports on the Dmap board and plug your programming/GPS Data lead into the primary port on the radio itself. The reason for doing it this way is that the primary port is the only one by which you can program your radio so if it's going to be connected to a computer in order to display the received GPS position reports, you might as well make this port the main one and then come the day you have to reprogram, you don't need to shuffle the leads around. You computer is already plugged into the main programming port.

One disadvantage of doing things this way is that the programming lead wasn't actually designed for GPS. It's purpose is to allow you to reprogram the radios when necessary. Because of this, one of the connections in the lead is intended to switch the radio on in situations where it doesn't have a control head fitted to allow you to do this. Repeaters are a case in point. Because this connection is automatically made when you insert the programming lead into the radio, it's still there when you leave it in place for GPS tracking. You may very well find that you can't now switch the radio off using the normal on/off switch on the control head. To fix this, you need to prevent pin 3 on the RJ45 connector from making contact. This was easy using the old serial lead but not so easy now sealed plug USB types are being supplied. The only way we can currently suggest to disable Pin 3 is to put a very thing sliver of plastic insulating tape over this pin on the RJ45 plug. Your on/off switch will now work correctly.

The Dmap boards described above are very good, they 'Just work' and seldom give any problems. They can also be reprogrammed to do a lot of other things if you can write code in C. If at all possible, the optimum method of extracting GPS data from your Simoco base radio is by using a Dmap accessory board.

There is a downside of course - they're very expensive. In fact they cost nearly as much as another SRM does.

A way around this is to use a different accessory board, the MA-ASIG. This has only one additional port which is actually all we need. There's a catch to using this board however and that's the fact that it comes in different configurations to do different jobs and guess what, the default configuration isn't the one we need. The configurations are set via a zero-ohm link field using surface mounted links smaller than a grain of rice. If you have a steady hand and the eyesight of a peregrine falcon then you can change these links yourself. The attached TMC document explains in detail how to go about this for the 'Dual Control Head' option which is what we need. Once the links have been changed, again, plug your control head into the MA-ASIG board port and the computer connection for GPS and programming goes into the original radio port.

You now have a base radio for voice and GPS tracking.
Next will be various ways of adding GPS tracking to your vehicles.

In fact, you can have both but it's not a method of operating a radio that most would go for. If the control head is completely removed, the SRM radio doesn't actually care and providing you don't ever want to change channel, you can fit a microphone and PTT to the facility connector at the rear of the set, the power connector in fact. Pin 7 will handle PTT and pin 14 allows microphone audio to be fed to the transmitter. Program for 'PTT Ext' in both cases and it will work OK. Now connect your computer to the normal RJ45 port and you have both voice transmission and reception plus base GPS decoding from the same SRM without any accessory boards needed. If you use a fixed channel repeater and never need to switch to other channels on that radio then this is the cheapest way of doing it. Use a desktop, 'goose-neck' microphone and that's all your base operator will need. No display, no nothing.
Rob_Brookes
 
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