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If the normal style of case is used then accessory boards can be fitted. As the repeater/rebroadcast function is now handled by the facility connector and not
the RJ45 sockets, these remain available for anything else you might want to fit. If a dual control head MA-ASIG board is fitted then both a control head and
a computer can be connected. If a Dmap board is used then you have three RJ45 ports available which gives you the ability to fit a computer and two control
heads if you need to, in a forward control vehicle for example.
To work properly, the second, 147.350 MHz radio, should be fitted with an independent power switch to enable it to be switched off when rebroadcast isn’t
required. This leaves the normal TWC radio available for standard comms. If the diplexer is fitted with an antenna changeover relay then any of the usual
rebroadcast configurations can be used to switch antenna between roof or mast . Using this method, a contact pin on the power connector isn’t needed to
achieve the antenna switching. The antenna relay can be powered up by the same switch that switches the secondary radio on so that as soon as the
rebroadcast system is powered up, the antenna is switched across to the one on your pump up mast etc.
If a cross-band rebroadcast device is used and is connected up in this manner then a diplexer isn’t required and any channel on the TWC radio can be
selected and used for both normal comms and rebroadcast. The low band link radio is only switched on when rebroadcast is needed.
The same antenna changeover relay can, incidentally, still be used without the diplexer if you need to transfer the antenna to a mast-mounted one when the
rebroadcast device is switched on.
There is a small amount of programming needed to use the SRMs in this way. Both TWC and the 147 or low band link radios are programmed in this way.
Here I’ve used ‘Carrier Detect’ but if you use CTCSS or Selcall muting then you should select ‘Valid Signal’. The methods described here have been tested
and proven to work but not every possible configuration of hardware and software has been tried. I’ll continue with this and update the post as new things
are tried.
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