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antenna. In transmit, the T/R line is open circuited to permit the transmitter signal to
generate a reverse bias on the diode to the peak value of the transmit signal.
C. Computer Board (Dwg. SS1967)
The computer board contains 3 basic sections:
1. Computer
2. Analog Processing
3. Channeling Circuits
1. Computer
The computer is comprised of the processor (I6), the Program Prom (I5), the Memory
Ram (I4), the address decoder (I7, the oscillator (I3), and the read-write decoder (I8).
The Ram contains a lithium battery that will support the memory indefinitely.
2. Analog Processing
The Analog Processing functions include noise detection, phone amplification, tracking,
squelch, Ident code filtering and transmitter monitoring.
I12B is an adjustable gain amplifier used to track receiver tuning to synthesizer
frequency. I12A and I12D is a 2-pole bandpass filter to separate noise from audio
signals. The noise is detected with D4. The noise level is used to inhibit the carrier
squelch threshold as determined by I13B.
I13A detects the voltage on the T/R switch. When a large negative voltage is detected, an
active signal is applied to I1 to turn on the transmit ‘tic’.
I11 is the NAV phone amplifier. I18 provides volume compression for the COMM audio
and I19 is the COMM phone amplifier.
3. Channeling Circuits
The channeling circuits are comprised of digital latches and output drivers. I16 provides
MHz output signals, the ILS Energize Signal and the VOR Test signal. I15 provides
KHz output signals. NPN transistors are used as output drivers. For Glideslope
channeling the drivers are connected directly to the output pins, for DME channeling
isolation diodes are provided in each line.
D and E. NAV (Dwg. SS1867) and COMM (SS1866) Receivers
The NAV and COMM receivers are functionally the same. The only difference between
the two receivers is the RF tuning, the AGC time constant and a tuning voltage sensor in
the COMM receiver which reduces the receiver gain during Transmitter actuation.
COMM Receiver tuning:
1. Connect a Synthesizer and Receiver combination to a NAV/COMM assembly.
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