2-10. RECEIVE AUDIO SIGNAL PATH. Continued
In the FH and PT mode, the FM DEMOD signal is a digital data stream.
It is routed to the ECCM module as BIT
SYNC DATA to be deinterleaved. (See paragraph 2-11.) The signal is sent through a digital-to-analog converter
to recover the original audio signal. The audio signal is returned to the switching module as RCV FH PT AUDIO
and continues along the RCV PT AUDIO path.
In the cipher text (CT) mode, the FM DEMOD signal is again a digital data stream. It is routed to the COMSEC
module as RCV CT. The COMSEC module decrypts the signal and recovers the audio signal. The recovered
audio (RCV CT AUDIO DECODED) is routed to the ICOM control module and back into the audio receive path.
In the FH and CT mode, the ECCM module deinterleaves the data stream. The data stream (FH DATA) is routed
to the COMSEC device where the audio signal is recovered.
2-11. TRANSMIT AUDIO SIGNAL PATH.
The transmit audio signal proceeds through the same modules as the receive audio signal only in reverse order.
See figure FO-4. The audio transmit (AT) signal is input at J3 or J4 pin D. A PTT is required for the transmit
The AT signals from J3 and J4 are summed by the ICOM data I/O module.
The audio signal is routed to an
automatic gain control (AGC) amplifier. If the switch is on, the gain of the AGC amplifier is increased.
The XMT AUDIO signal is routed through the ICOM control module to the ICOM power supply. The ICOM power
supply combines the XMT AUDIO signal with the 150-Hz squelch tone.
From there it is routed through the
switching module to the exciter/power amplifier.
A PTT at J3 is routed through the fill routing module to the ICOM control module. See figure FO-4. A PTT at J4 is
routed directly to the ICOM control module. Both are combined to generate the AUDIO MDL PTT-N. It is buffered
by the ICOM power supply and sent to the control module and the switching module.
When operating in the FH mode, the XMT AUDIO signal is routed from the ICOM power supply to the ECCM
module prior to the addition of the 150-Hz squelch tone. The ECCM module converts the XMT AUDIO signal into a
digital data stream (FH DATA). The FH DATA signal goes to the switching module where it is amplified and routed
to the exciter/power amplifier module.
When operating in cipher text, the XMT AUDIO signal is routed from the ICOM control module to the COMSEC
module. The CT XMT signal that is returned is a digital data stream.
2-12. RECEIVE DATA SIGNAL PATH.
The RT can receive audio data and digital data. Audio data can be processed using either AD1 or TF. When the
RT is set to use AD1, the analog data signal follows the audio receive path. When TF is used, the analog data is
converted into 16 kb/s digital data by the transmitter. The receiver converts it back into analog data. Low speed
digital data (600 b/s to 4.8 kb/s) is also transmitted as 16 kb/s digital data.
Majority logic error correction is
provided for TF and low speed digital data.
The ICOM control module performs the data rate conversion and
The RADIO PTT-N line is held at logic 1 during receive mode. The data signal is recovered from the carrier by the
RF section, which routes it to the switching module as FM DEMOD. See figure FO-5. A crossover detector
senses the presence of the signal.
The bit sync/digital squelch network synchronizes the local clocking with the data. When synchronized, the
BS/TONE SQUELCH line is set to logic 1. PT DIGITAL CLK provides clocking for the data signals. It is a 16-kHz
square wave, at logic 0/1 levels, that is generated by the switch control. RCV PT DATA and PT DIGITAL CLK are
routed to the ICOM I/O section of the RT. The data and clocking signals are buffered and routed to the ICOM
control module. ICOM control processes and switches the signal through to the ICOM data I/O module.