BASIC RCU SIGNAL TYPES.
There are four basic signal types used in the RCU:
Analog signals include the audio and analog data signals. They can vary greatly in signal level, shape, and
Digital signals include the timing clocks and digital data signals. The clocks are used to synchronize the serial
digital data streams between modules. Within the RCU they are typically at logic 0 and logic 1 Ievels. Logic 0 is
-0.5 to 0.5 V dc. Logic 1 is 5.2 to 6.2 V dc. Clock frequencies vary. RCU I/O digital signals use the +5 V logic
levels as required by MlL-STD-188-114. Logic 0 is 5 V dc. Logic 1 is -5 V dc.
Control signals include the status and control lines. They will be set to logic 1 to indicate or direct a particular
condition. In some cases, a signal name includes a -N to indicate that the logic is reversed. For example, a
logic 1 on the PTT-N line indicates the absence of a PTT; logic 0 indicates a PTT.
Power signals are at constant V dc levels. Most are provided by the power supply as described in paragraph
12-5. The ICOM power supply provides the voltages used by the ICOM I/O section.
ANALOG RECEIVE SIGNAL PATH.
SC PT analog is FM modulated onto the 40-kHz carrier by the RT and input to the RCU on the TWO-WIRE I/O line.
See figure FO-20. It is demodulated by the two-wire interface, output on the RCU RCV ANLG line, and routed to
the bit sync switching module. FH MODE is a logic 0 and switches RCU RCV ANLG through a summing network
where it is output on the RCV PT ANLG line. RCV PT ANLG is switched through the ICOM power supply when RCV
PT/CT SEL is a logic 0, and is output as RCV PT ANLG/R. RCV PT ANLG/R is routed to the ICOM control module
where it is routed through four switches. These switches are controlled by RADIO PTT-N/R (which is a logic 1 in
receive), RCV PT/CT SEL/R (which is a logic 0 in PT), and ST/SQ/R which is a logic 0 when the RCU is not
transmitting and the 40-kHz DET output of the two-wire interface is a logic 1. RCV PT ANLG/R is then output to the
ICOM data I/O module on the RCV ANLG/SIDETONE line. The received audio is routed through a summing
network, a filter, and is routed to the front panel VOL control. The variable audio is routed back to the ICOM data
I/O module through the volume amplifier and is routed to two switches. These switches route the audio to the
AUD/FILL and AUD/DATA connectors when FILL SEL-N/R is a logic 1, and DATA I/O EN is a logic O respectively.
FILL SEL-N/R is an output from the fill routing module and is a logic 0 when a fill device is attached. DATA I/O EN is
an output of the ICOM control module and is a logic 1 when digital data, TF, or AD1 is received.
FH PT analog is FSK modulated onto the 40-kHz carrier by the RT, demodulated by the two-wire interface, and is
output on the 40-kHz XMT DATA line at digital levels. 40-kHz XMT DATA is routed to the bit sync switching module
where it is synchronized to the 16-kHz CLOCK and is output as BIT SYNC DATA. BIT SYNC DATA and the 16-kHz
CLOCK are routed inside the bit sync switching module to a digital-to-analog converter where the BIT SYNC DATA
is returned to an analog signal. The output of the converter is routed to the other side of the switch that picks up
RCU RCV ANLG. When FH MODE is a logic 1, the output of the converter is switched to a summing network and is
output as RCV PT ANLG. FH PT analog is then routed along the same path as SC PT analog. The ST/SQ/R input to
the ICOM control module iS a logic 0 when the ACQ/TRK #1 output from the bit sync switching module is a logic 1
in receive FH PT analog.