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TM 11-5820-890-30-5
2-12. RECEIVE DATA SIGNAL PATH. Continued
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 audio section of the RT.
The data and clocking signals are buffered and routed to the audio control module. Audio control processes and
switches the signal thru to the audio/data l/O module. The signals are amplified to the correct levels and output to
the RT AUD/DATA connector (J4). DIGITAL DATA RCV (DDR) and DIGITAL DATA CLK OUT (DDCO) output signal
levels are 5 V for logic 0 and -5 V for logic 1. Analog data signal levels are 0.77 Vrms ±3 dB.
When operating in FH mode, data received signals are routed through the ECCM module. The switching module
sends the bit synchronized data (BS DATA) to the ECCM for deinterleaving. FH DATA is returned to the data
receive path.
Receive data cipher text (RDCT) is routed to the COMSEC connector from the switching module when the RT
operates in cipher text mode. The COMSEC device decodes the signal and returns the data receive signal
(AR/DDR) to the audio control module. The COMSEC device generates a clock signal for the data (AT/DDCO)
and routes this to the audio control module also.
Each data transmission is preceded by a sync preamble. This preamble is generated by the data rate adapter
section of the ICOM control module, It provides a synchronization source, tells the RT a data transmission is
being received, and whether the signal is plain or cipher text. During receive mode, the data rate adapter section
monitors the RCV DATA output from the audio control module. When the preamble is detected, the NO CODE
DETECT line will set to logic 0. CODE X/R ENBL is at logic 1 during preamble detection.
When the DATA switch is set to AD2 or one of the other data rates, the audio control module sends the signals to
the data rate adapter (RCV DATA and RCV CLK). The data and clock signals are converted to LO-SPD DATA and
LO-SPD CLK. LO-SPD DATA SEL-N at logic 0 switches these LO-SPD signals back into their proper paths.
The AD2 signal is tapped from the LO-SPD DATA line. It is shaped by an RC circuit into the necessary analog
signal by the audio/data I/O module.
2-13. TRANSMIT DATA SIGNAL PATH.
The RT can process analog data and digital data. Analog data is input on J4 pin D (AT/DDCO). See figure FO-6. If
the data rate is set to AD2, J4 pin F (ADMC/DDT) must be grounded for proper operation. The analog data signal
will be converted to 16 kb/s digital data by the RT. If the data rate is set to AD1, the signal follows the audio path.
Digital data is input on J4 pin F (ADMC/DDT). Pin E (DDMC) must be grounded. The RT provides a clock on J4 pin
D (DDCO) and the digital data signal must be synchronized with the clock.
For AD2, the analog data signal must be FSK modulated at 1200/2400 Hz. It is routed through the audio/data I/O
module. An AGC amplifier and limiter adjust the level and the signal is output as LIMITED ANALOG DATA. The
audio control module demodulates the FSK signal to convert it into a low speed digital signal. This signal is routed
through the data rate adapter section where it is converted into a 16 kb/s digital data stream (XMT DATA). It is
routed to the audio power supply where the signal is buffered and then routed through the switching module to
the exciter/power amplifier.
The digital data transmit (DDT) signal will be input as a ±5 V square wave, It is converted to logic 0/1 levels by the
audio/data I/O module. The logic 0/1 level signal (DIGITAL DATA XMT) is routed to the audio control module. If it
is anything other than 16 kb/s, it is routed to the data rate adapter section. It converts the data rate to 16 kb/s and
returns the signal. The signal is routed to the audio power supply where it is buffered and sent to the switching
module. The switching module routes the signal to the exciter/power amplifier.
2-16
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