Technical data

B KY 96A, KY 97A
Rev 5, Apr 2003 MM 006-05674-0005.dwd Page 4-6
4.3.2.1 Synthesizer
The stabilized master oscillator is based around synthesizer I103 which is serial pro-
grammable by the microprocessor.
A 3.975 MHz crystal is attached to the gate oscillator, and the reference divider divides
it by 159 to produce the 25 kHz reference frequency. The RF frequency is divided by
the internal pre-scaler and divider then compared by the phase detector to the refer-
ence frequency. If the frequency is greater than 25 kHz the phase detector will pulse
up once every 40 usec. If the frequency is less than 25 kHz the phase detector will
pulse down. The greater the divided frequency from the reference frequency the wider
the phase detector pulse.
Q133, R137, and C135 integrates the lock detect pulses to send the lock detect signal
to the microprocessor. The reference oscillator is lightly coupled to Q132 which am-
plifies the 3.975 MHz signal for the microprocessor and I705 on the processor board.
The clock, data and strobe lines are driven from the microprocessor.
4.3.2.2 Voltage Translator
Q134, Q135, Q136, Q137 and their associated parts make up the voltage translator.
The voltage translator translates from five volt pulse to nine volt pulse and inverts the
logic of the pulses. The output of the phase detector is fed to the emitters of Q134 and
Q135. The bases of Q134 and Q135 are biased to about 2 volts so that when the
phase detector is tri-stated, Q134 and Q135 will be off. If the phase detector pulses
low, Q134 will turn on causing Q136 to turn on and a 9 volt pulse to appear at the out-
put of the voltage translator, TP110. If the phase detector pulses high, Q135 will turn
on causing Q137 to turn on pulling the output to ground.
4.3.2.3 Low Pass Filter
The low pass filter is a lead/ lag network with a 2.5 kHz elliptical low pass filter with its
notch at 25 kHz. C235 and C236 make up the elliptical filter. R279, R280, R281, and
C237 make up the lead/ lag network. With this filter, the loop bandwidth is about 300
Hz and the 25 kHz notch is about 130 dB down. The control voltage is fed to the pre-
selector through R136 and to the VCO through L132.
4.3.2.4 Voltage Controlled Oscillator (VCO)
Q108 and its associate parts form a modified Hartley oscillator. The varactor CR101E
is part of a matched set of five varactors so the preselector will track the VCO. C149
determines the range of the tuning voltage, the smaller the capacitor the larger the tun-
ing range must be to maintain the same frequency range. C249 and R299 provide
bias stability. The tuning range is 118.00 MHz at 2.5 V and 151.375 MHz at 8.0 V.
4.3.2.5 VCO Buffer
Q109 and its associated parts form the VCO buffer. The VCO buffer provides isolation
from the transmit buffers and the mixer as well as amplifying the signal to about +7
dBm to the mixer.