TTI TCB-550, Service Manual

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4-3-1. Introduction
The synthesizer is implemented with the following companents :
IC6 is a CMOS LSI that includes most of PLL block. The VCO with varicap diode DV1,2 as
a part of the oscillator tank circuit.
QV2 is a switching transistor to connect or disconnect the tunning capacitor in the VCO oscillator
tank circuit for transmitter or receiver.
The crystal, X2(10.24MHz) and other components at PIN 1 and 24 of IC6 can make a reference
frequency oscillator with internal amplifier.
The oscillator output is internally fed to a divied by 4096 to produce A 2.5KHz swuare wave witch
is the reference input to the phase detector.
QV1 is connected as a hartley type oscillator with varicap diode as part of the tank circuit. With
Appropriate control voltage on D601 the VCO can be oscillate over the required range of
13.4825MHz to 16.710 MHz.
4-3. Description Of Each Block
4-3-2. Reference frequency
PLL IC (IC6)
X-TAL(X2)
VARICAP DIODE(DV1,2)
4-3-3. VCO
The programmable inputs for each channel are set by the PLL clock(PIN34), DATA(PIN35),
Enable(PIN33) of IC5.
Each input signal to control the PLL IC is done with the provided key input PIN 12~15.
For each key input, an internal code convert EEPROM provides the appropriate control to the
programmable divider for that channel.
Since the change transmit and receive, and additional BIT is required ar PIN 16 of IC5 to allow
the ROM to recognize the status TX or RX.
During transmit the push to talk switch grounds PIN 16 thru diode(DS1) which is the transmit
status.
Thr programmable divider output is fed to the phase detector for comparison with the 2.5KHz
reference. See TABLE 1 for actual input and divide ratio on all channels.
The phase detector is a digital phase comparator which compares the phase of the reference
woth programmable divider output square waves and develops a series of pulses whose DC
level depends on the phase error of each signal.
The phase detector pulse output is fed to an active low pass filter and RC LPF ouput signal
of IC6 is filtered and fed to varicap DV1,2 control the VCO frequency.
4-3-4. Programmable divider and its control
4-3-5. Phase Detector and VCO control