12-3. ICOM I/O SECTION. Continued
Figure 12-4. ICOM I/O Section Module Locations
The bit sync switching module is mainly digital and operates solely on received PT signals. It performs synchroni-
zation of digital signals, converts received FH voice to analog, provides an intercom alarm, and switches re-
ceived analog signals.
Received digital data from the two-wire interface and a 16-kHz clock are synchronized by the bit sync switching
module. Three outputs are provided to the main switching module when digital data is received. These are the
synchronized digital data and 16-kHz clock and a digital squelch signal which is a logic 1 when synchronization
has been accomplished. The main switching module switches the data and clock back to the ICOM I/O section
after synchronization. The 16-kHz clock is derived by the bit sync switching module from the 640-kHz system
clock from the control module.
When the RT is receiving an FH voice signal, it is sent to the RCU over the two-wire link as a digital signal, and is
routed to the bit sync switching module via the two-wire interface. The bit sync switching module uses the digital
synchronization network and a digital-to-analog converter to return this signal to analog.
SC voice is sent to the RCU by the RT as an analog signal. This signal is output to the bit sync switching module by
the two-wire interface. A 1.2-kHz digital clock is input from the main switching module to the bit sync switching
module, where it is converted to analog for use as an intercom alarm. This alarm is used to tell the RCU operator
that the RT is receiving an RF signal while operating in the ICM mode.
Receive FH voice, receive SC voice, and the intercom alarm are switched by the bit sync switching module to a
single analog output, which is routed to the ICOM power supply. The various switch controls are provided by the
The ICOM power supply is the red/black boundary in the RCU. The red section contains signals that have not yet
been encrypted by the COMSEC module and must be isolated from the black section which contains signals that
have already been encrypted by the COMSEC module.