MRMap Development Team 10/01/2009
Summary:
The system described here has been run at full power around the Kendal area. I have an antenna
at both ends of the house roof for testing things like this and the 147MHz link was only transmit-
ting down the length of the house. However the TWC radio was required to operate to a moving
vehicle several miles away and no polls or replies were missed. All the types of polling of GPS
equipped radios was tried and several handsets were operated alongside the rebroadcast unit.
Not all of these were SRP9100s or indeed, Simoco radios and in none of them was the FFSK
data audible when CTCSS was enabled on receive and transmit.
All received data, be that at the ‘base’ end or in the vehicle itself, was completely silent but voice
transmissions were received normally although the usual squelch tail was thankfully absent.
The amount of wiring needed in the power/facility connectors is not great and is easily done by
anyone who can wield a soldering iron. This can be taken a stage further if required as LED op-
eration indicators can be wired to the same pin 8 and ground.
Still to do:
Firstly I need to check that the same system also works with a cross band rebroadcast unit.
(Done)
Next, will it work with an SRM-based, duplex repeater as against a rebroadcaster?
Hopefully finally, I need to re-introduce the ability to change channel in the cross band rebroad-
cast. This is lost due to the absence of the red crossover lead in this system. However, TMC in
Australia advise me that the rear, facility connector PTT lines take precedence over the RJ45
crossover cable. The audio connections on the RJ45 X-over cable are not required and can be
left out as can all the other connections on this cable except those on pins 1 and 2. These two are
the data connections that handle the remote channel changing instructions in a cross-band re-
broadcast.
Unfortunately they are also the connections that handle PTT when this cable is used to facilitate
rebroadcast or repeater operation, however, TMC did say that the rear facility connector takes
PTT precedence. So far I don’t know whether this is correct but as soon as I’ve wired up a quick
two-wire cable (!) I’ll give it a go. (Done)
One last thing, even though the FFSK speaker mute on Simoco radios does satisfactorily remove
90% of the data noise, it’s still very weird to see the plot move or watch ‘GPS Poll’ come up on
the radio display but to hear absolutely, and that really is absolutely, nothing. For ten years now
I’ve been listening to radios beep away at me and now it’s gone, I quite miss it.
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