7
The various radio configurations used to form
rebroadcast devices are taken from information
provided by TMC Radio Pty Ltd in Australia.
They are the manufacturers of the ‘Simoco
SRM9000’ series radios. Rebroadcast can be
achieved using other manufacturers hardware
but the extremely simple way in which this is
achieved with SRM9000’s, and the number of
variations available for experimentation, means
they are hard to beat under these circum-
stances.
All re-broadcast units require two radios.
One on the team working channel (TWC) and another
On the re-broadcast channel shown here as a
hypothetical Low Band (68 to 88 MHz) channel
TWC
Low Band
The two SRM9005’s require only a special cross-linking cable connected between the front-mounted RJ45 jack sockets, in order to be-
come a rebroadcast device. The rebroadcast mode is automatically selected once the cable is fitted and both radios are switched on. See
the next page for details of the cable.
This is fundamentally the same for all variations on the system. Two radios connected by a crossover cable.
Using the configuration shown, the Team Working Channel (156.175 to 161.875 MHz) is converted and simultaneously re-transmitted on a suitable low band
frequency. 86.3125 MHz for example as is used in Scotland. Whatever the frequencies used, the system adopted is called ‘Two-Frequency-Simplex’ . That
is, two separate frequencies are used in the system, one in the primary radio and another in the secondary radio. Each radio both receives and transmits on
it’s programmed frequency hence is simplex in operation. All persons listening to either of the two radios will hear both sides of the conversation and each
other. The rebroadcast device converts one frequency to the other and re-transmits it.
The above circuit is the simplest form of this device and requires no other hardware apart from power and aerials. The operating channel of the TWC radio
can
be changed but this requires that a 9025 telephone handset or a similar control head, is plugged into the socket occupied by the cross-over cable so is
obviously not a permanent feature. Basically, this device is meant to operate on one TWC only.
The Simoco 9025 telephone handset control head
and magnetic mounting plate
Very Basic Rebroadcast
There are no UKSAR low band channels available but a number of teams have now pur-
chased their own frequencies from Ofcom for this purpose and under these circum-
stances, this is a viable solution to the problem.
“Cross-Band” Re-Broadcast.
Defined as :- Each radio operates in a different part of the radio spectrum, here, high band and low band. They therefore don’t interfere with each other.
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