RECEIVE RF SIGNAL PATH. Continued
Figure 2-9. Antenna Connector Schematic
Keying and frequency selection are controlled by the control module. During receive, the T/R line is held at logic
0. The operating frequency is distributed using the SERIAL DATA line. TUNE GATE-N and TUNE CLK are used to
decode the SERIAL DATA.
The RF signal from the impedance matching network goes to the exciter/power amplifier. After passing through
a low-pass filter, it is routed to the tuner/mixer. The tuner/mixer filters and amplifies the RF signal and then mixes
it with the local oscillator (LO) signal from the synthesizer.
The LO is 12.5 MHz higher than the operating
frequency. The tuner/mixer and synthesizer are digitally tuned using the SERIAL DATA line. The 12.5 MHz IF
signal is routed to the lF/demodulator. The lF/demodulator demodulates the IF signal to recover the baseband
audio or data signal (FM DEMOD).
The SIG display is driven by the SIG STR RCV signal from the lF/demodulator. The SIG display should respond as
RF Level at ANT Connector
-121 to -102
-112 to -92
-102 to -82
-92 to -72
-82 to -20
Increase in sequence
5, 6, 7
The signal path is unchanged for FH operation. A SYNC CODE signal is recovered from the received signal and
used to synchronize the receiver with the transmitter. DATA SW-N, HOP TIME, and WB SEL are control lines from
the ECCM module used during FH operation. DATA SW-N is held at logic 1 during FH operation. HOP TIME goes
to logic 1 while the frequency is being changed. WB SEL (wideband select) goes to logic 0 when the RT looks for
a CUE signal.
If a CUE signal is detected, the lF/demodulator sets the CUE PRESENT line to logic 1.