Kenwood TKR-850 Service Manual page 21

4. PLL Frequency Synthesizer
The PLL frequency synthesizer circuit consists of the fol-
lowing circuits : 4-1 receiver PLL circuit, 4-2 transmitter PLL
circuit, and 4-3 unlocked detector circuit.
4-1. Receiver PLL
The receiver PLL circuit is located in VCO unit A3 (X58-
480) on TX-RX unit (X57-627 A/2), and consists of VCXO X2,
VCO's (Q350 and Q351), a single-chip PLL IC IC300, buffer
amplifier Q355, and high-frequency amplifier Q302.
The VCXO generates 16.8MHz. The frequency stability is
within ± 1.5ppm (Temperature range of –30 to +60°C). The
frequency tuning of the VCXO is done to apply a voltage to
pin 1 of the VCXO. The output of the VCXO is applied to pin
8 of the PLL IC through the pin 7 of the VCO.
The first local oscillator is a lower heterodyne local oscil-
lator, and the VCO oscillator frequency is 405.15 to
435.15MHz (K), 435.15 to 467.15MHz (K2), 355.15 to
385.15MHz (K3), 395.15 to 425.15MHz (E).
The oscillator frequency is controlled by applying the
VCO control voltage, obtained from the phase comparator to
the varactor diodes.
VCO unit (X58-480)
Q350
VCO A
Q354
SW SW Q352
SW Q353
SRR
VCO B
Q351
Q300
IC300
LPF PLL-IC
CP,DP
EPR,LDR
µ-com
IC604
Fig. 5 Receiver PLL
CIRCUIT DESCRIPTION
TX-RX unit
Q355
AMP
Q302 X2
VCXO
AMP
4-2. Transmitter PLL
The transmitter PLL circuit is located in VCO unit A2 (X58-
481) on TX-RX unit (X57-627 A/2), and consists of VCXO X3,
VCO's (Q350; K,K2,E type, Q351; K3 type), a single-chip PLL
IC IC300, buffer amplifier Q355, and high-frequency ampli-
fier Q302.
The VCXO generates 16.8MHz. The frequency stability is
within ± 1.5ppm (Temperature range of –30 to +60°C). The
frequency tuning and modulation of the VCXO are done to
apply a voltage to pin 1 of the VCXO. The output of the
VCXO is applied to pin 8 of the PLL IC through the pin 7 of
the VCO.
The VCO oscillator frequency is 450.00 to 480.00MHz
(K), 480.00 to 512.00MHz (K2), 400.00 to 430.00MHz (K3),
440.00 to 470.00MHz (E).
The oscillator frequency is controlled by applying the
VCO control voltage, obtained from the phase comparator to
the varactor diodes.
4-3. Unlock Detector Circuit
If a pulse signal appears at the LD pin of IC300, an unlock
condition occurs, causing the voltage applied to the pin of
the microprocessor to go low. The names of this pin are
LDT for TX PLL and LDR for RX PLL. When the micropro-
cessor detects this condition, the transmitter is disabled.
VCO unit (X58-481)
Q350 : K,K2,E
VCO A
MO
Q351 : K3
VCO B
MO
Q300
IC300
LPF PLL-IC
CP,DP
EPT,LDT
µ-com
IC604
Fig. 6 Transmitter PLL
TKR-850
TX-RX unit
Q355
AMP
MO MO
Q302 X3
VCXO
AMP
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