User's Manual
DMR_Manager Operating Manual 2011/07/04 Version 1v2
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Page 8 of 51
2.4.1 SYNCHRONIZATION, VOTING AND EQUALIZATION
Simulcast radio network are able to realize the maximum radio coverage of the territory with minimum use of
radio frequency.
In a simulcast network, unlike a cellular system in which each cell is characterized by a particular frequency, all
the terminals operate at the same frequency, like a big cell.
Therefore it is necessary that the carriers of all transmitters are frequency locked and phase coherent with the
master one.
Frequency synchronism of the
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station can be extracted from multiple sources, depending on
network needs and the references availability, and transmitted to all the base stations from the master one.
This signal is received from all the satellites that reset their clock on it.
In this way all satellites are zeroed in frequency compared to master and then zeroed between them.
If there is not a good frequency synchronization the quality of communication considerably decreases in the
equal fields strenght areas.
Another essential function of
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simulcast networks is the voting, which is the method by which
the best signal received from the network is continuously selected. The signal voted is sent to the satellite and
then diffused in the whole coverage area.
Simulcast networks require also particular attention in the choice of media linking the various stations. The
characteristics of these media must be such as to make as much as possible identical signs of low frequency
(audio) that each station must retransmit.
For that reason simulcast networks made by
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employ equalization devices based on Digital
Signal Processing, which are able to automatically minimize the differences between the media paths
This feature allows to use a large family of communication media, including time-varying lines as pupinized
copper, presenting considerable variations in temperature, or as non-dedicated telephone lines and therefore
subjected to variations of delay and BF response.
.
TRX
VHF
TRX
VHF
TRX
VHF
RF broad.
Km_2
RF broad.
Km_1
RF broad.
Km_0
MUX_1
delay
MUX_2
delay
SLAVE2
SLAVE1
MASTER
Linear simulcast network configuration