BENDIXKing KY 96A, Maintenance Manual

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B
KY 96A, KY 97A
Rev 5, Apr 2003 MM 006-05674-0005.dwd Page 4-8
4.3.3.5 Modulator (14 Volts KY 97A)
The audio signal is applied to the primary of T108, which has a 4 to 1 turns ratio. This
steps up the voltage swing on the modulator transistors Q124 and Q125 enough to
make a 0 to 12 V swing to the transmitter final and driver. This output is also fed back
to the modulator compressor. The mod bias is fed to the secondary of T108 providing
the bias to Q125 with R247 being the current limit resistor.
4.3.3.6 Modulator (28 Volts KY 96A)
The audio signal is applied to the primary of T108, which has a 4 to 1 turns ratio. This
steps up the voltage swing to the bases of the modulator transistors Q124 and Q130
enough to make a 1 to 12 V swing on the transmitter final and driver. This output is
also fed back to the modulator compressor. The mod bias is fed to the secondary of
T108 providing the bias to Q124 and Q130 with R247 being the current limit resistor.
4.3.4 Transmitter
4.3.4.1 RF Amplifier
RF is fed from the transmit buffers to the RF amp, on the transmitter board, through a
miniature 50 ohm coaxial cable. The drive level is approximately 15 dBm. During re-
ceive the RF is attenuated as the TX(not) line goes high it turns on Q404 shorting the
drive to ground and removing the bias from pin diode CR403 to “OPEN” the input to
Q401. During transmit, the base current is supplied through R401 and CR403 to op-
erate Q401 class A. Transformer T401 is broadband tuned and steps the collector im-
pedance down to the input impedance of the driver.
4.3.4.2 Driver Q402
RF drive is fed through C412 and C437 to the driver, Q402. The driver is operated
class C and the collector is modulated through T402. The collector is broadband tuned
and is coupled to the final by T402.
4.3.4.3 Final
Capacitor C415, C416, and C440 form the input matching network for the final power
amplifier, Q403. The final is operated class C and is modulated at the collector. The
low collector output impedance is stepped up to approximately 50 ohms by transform-
er T403.
4.3.4.4 Low Pass Filter
A three section elliptical low pass filter is placed between the final and the antenna to
attenuate all harmonics which may be generated in the transmitter. During transmit
the T/R diodes CR401 and CR402 are reversed biased to protect the receiver from 5
watts of power.
4.3.5 Microprocessor
4.3.5.1 Communication to Synthesizer PLL I702