LOCAL OPERATION
3-78
DCS
Overview
Digitally Coded Squelch signaling is a system for addressing mobile radio transceivers from their
base station by transmitting a code unique to the addressed transceiver for the duration of the
transmission. The principles and limitations of the system provide 104 uniquely identifiable codes
for use on any one RF channel.
The coded signal consists of a repeating 23 bit word that has error correcting information and
timing using 14 bits, leaving nine bits available to carry address code.
The digital signal is formatted as a simple non-return to zero (NRZ) signal, which is used to
directly modulate the transmitter. On frequency shift modulating systems a ‘1’ is usually made to
increase the carrier frequency and a ‘0’ to decrease the carrier frequency. An ‘Invert’ facility is
included to reverse the polarity of the digital signal before it is applied to the modulator.
The most often used bit rate for generating the 23 bit code words and that which is specified in
most standards is 134 bits/s. This allows the system to operate below the communications audio
pass band.
See Signal routing and RF input attenuators starting on page 3-70.
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