ANALOG RECEIVE SIGNAL PATH. Continued
CT analog is demodulated by the two-wire interface and is output at logic Ievels on the 40-kHz XMT DATA line.
This line is routed to the COMSEC module as RDCT. The COMSEC module synchronizes RDCT to an internal
clock, decrypts the message, and outputs digital signals DDR and DDC. The ADMC-N and DDMC-N lines are both
logic 1 in receive analog and the COMSEC module removes the sync pulses placed in the message by the
transmitter in the dead spots during the voice transmission, The DDR and DDC lines are inputs to a
digital-to-analog converter which outputs the analog signal AUDIO RCV. AUDIO RCV is input to the ICOM control
module, where it is routed to the RCV ANLG/SIDETONE output. RCV PT/CT SEL/R is a logic 1 and ST/SQ/R is a
logic 0 when the CDSQ-N output of the COMSEC module is a logic 0, indicating a CT reception.
ANALOG TRANSMIT SIGNAL PATH.
Transmit audio from a handset is input to the RCU on pin D of the AUD/FILL or AUD/DATA connector. See figure
FO-21. AT/DDCO from the AUD/DATA connector is switched to the input of a summing network when DGTL CLK
OUT EN-N is a logic 1. DGTL CLK OUT EN-N is a logic 0 when the RCU is transmitting or receiving digital data and
switches a clock out to the digital data device. AT/FILL INFO from the AUD/FILL connector is switched to the input
of the summing network when FILL SEL-N/R is a logic 1. FILL SEL-N/R is a logic 0 when a fill device is attached and
switches FILL INFO to the fill routing module. The output of the summing network is input to an amplifier/filter,
where output level is controlled by an automatic gain control circuit. When the VOL switch is pulled out, the gain
of this circuit is increased, allowing lower audio input Ievels. The fixed level output, XMT ANLG, is routed to the
ICOM control module for PT transmit and to the COMSEC module for CT transmit.
in PT analog transmit, XMT ANLG is routed through a switch in the ICOM control module and is output on the XMT
PT ANLG/R line. This switch is controlled by RCV PT/CT SEL/R, which is a logic 0 in PT. XMT ANLG is also routed
through three switches and is output on the RCV ANLG/SIDETONE line as sidetone. The controls are RADIO
PTT-N/R which is a logic 0 in transmit, RCV PT/CT SEL/R which is a logic 0 in PT, and ST/SQ/R which is a logic 0
when sidetone is enabled. in transmit, the ST/SQ/R line iS controlled by the SIDETONE DSBL output from the
control module. Sidetone is enabled when SIDETONE DSBL is a logic 0 and disabled when it is a logic 1.
The PTT-N line from the AUD/FILL connector is routed through a switch in the fill routing module and is input to the
ICOM control module. The PTT-N line from the AUD/DATA connector is routed directly to the ICOM control
module. Both of these lines are debounced and input to a PTT circuit. The outputs of this circuit are
COMSEC PTT-N and AUD MOD PTT-N/R.
AUD MDL PTT-N/R is routed through the buffer on the ICOM power supply and is input to the main switching
module, where it is output as RADIO PTT-N. RADIO PIT-N is routed through the ICOM power suppIy into the ICOM
control module, where it controIs the above mentioned switches.
XMT PT ANLG/R is routed through a switch on the ICOM power suppIy. The switch is controlled by the PT/CT SEL
output from the COMSEC module. PT/CT SEL mirrors the front paneI COMSEC switch and is a Iogic 1 in CT and a
Iogic 0 in PT. XMT PT ANLG/R is switched to the XMT PT ANLG output when PT/CT SEL is a logic 0.
The XMT PT ANLG output from the ICOM power suppIy is routed to the two-wire interface where it is FM
modulated onto the 40-kHz carrier for transmission to the RT. The 40-kHz A/D SEL line selects the XMT PT ANLG
input to the modulator when it is a logic 1, and seIects the PT/CT DGTL OUT input when it is a logic 0. The 40-kHz
A/D SEL is controlled by the controI moduIe. The moduIated 40-kHz carrier is switched to a transmitter amplifier
by the 40-kHz XMT ENBL Iine, which is an output of the controI module. This line is a Iogic 1, which enabIes the
carrier when the RADIO PTT-N input to the controI moduIe is a Iogic 0. The output of the transmitter amplifier is the
TWO-WIRE I/O Iine to the RT.