BENDIXKing KY 96A, Maintenance Manual

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B
KY 96A, KY 97A
Rev 5, Apr 2003 MM 006-05674-0005.dwd Page 4-3
4.3 DETAILED THEORY OF OPERATION
Refer to schematics in Section VI of this manual.
4.3.1 Receiver
4.3.1.1 Antenna Input Circuit
In the receive mode Q101 is switched on, forward biasing the T/R diodes located on
the transmitter board. The desired signal passes through the first pole of the low pass
filter, then to the T/R diodes, and then to the receiver board. C102 steps up the im-
pedance to match the first pole of the preselector.
4.3.1.2 Double Tuned Preselector
The first pole of the preselector is tuned by L101, C103 and CR101A. The signal is
coupled to the second pole of the preselector by L102. The second pole of the prese-
lector is tuned by L103, C106 and CR101B. The matched varactor diodes, CR101A
and CR101B, are tuned to the desired frequency through a large resistor from the VCO
control voltage. The desired signal is coupled to gate 1of the RF amplifier by C107.
4.3.1.3 RF Amplifier Q102
Q102 and the associated parts make up the RF amplifier. The desired signal is ap-
plied to gate 1. The RF AGC is applied to gate 2. The RF amplifier has 20 dB of gain
at maximum RF AGC voltage, and 30 dB of attenuation with minimum RF AGC volt-
age; producing a dynamic range of 50 dB. C114 couples the desired signal to the dou-
ble tuned interstage.
4.3.1.4 Double Tuned Interstage Network
The first pole of the interstage network is tuned by L105, C115 and CR101C. The sig-
nal is coupled to the second pole of the interstage network by L106. The second pole
of the preselector is tuned by L107, C118 and CR101D. The matched varactor diodes,
CR101C and CR101D, are tuned to the desired frequency through a large resistor
from the VCO control voltage. The desired signal is coupled to gate 1 of the mixer
through L133.
4.3.1.5 Mixer Q103
Q103 and the associated parts make up the mixer. The local oscillator signal is fed to
gate 2 at a frequency 11.4 MHz above the desired signal. The level of the local oscil-
lator is b4 dBm and +7 dBm. The desired signal is now at 11.4 MHz. The
drain of Q103 is tuned to 11.4 MHz by T101 and matched to the crystal filter.
4.3.1.6 Crystal Filter FL101
The crystal filter provides the desired selectivity. The input and output of the filter is
matched to 4100 ohms by T101 and T102 respectively.
4.3.1.7 First IF Amplifier I101