Kenwood TKR-850 Service Manual page 14

TKR-850
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 (X57-696 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 oscilla-
tor, and the VCO oscillator frequency is 405.15 to 435.15MHz
(K), 395.15 to 425.15MHz (E), 435.15 to 467.15MHz (K2) or
355.15 to 385.15MHz (K3).
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
SW
SRR
VCO B
Q351
Q300 IC300
LPF PLL-IC
CP,DP
EPR,LDR
µ-com
IC604
Fig. 5 Receiver PLL
14
CIRCUIT DESCRIPTION
TX-RX unit
Q355
AMP
Q352
Q353
Q302 X2
VCXO
AMP
TX VCO
(X58-481)
RX VCO
(X58-480)
Fig. 7 VCO oscillation frequency
4-2. Transmitter PLL
The transmitter PLL circuit is located in VCO unit A2 (X58-
481) on TX-RX unit (X57-696 A/2), and consists of VCXO X3,
VCO's (Q350 : K,K2,E, Q351 : K3), 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 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),
440.00 to 470.00MHz (E), 480.00 to 512.00MHz (K2) or
400.00 to 430.00MHz (K3).
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 microprocessor de-
tects this condition, the transmitter is disabled.
VCO unit (X58-481)
Q350 : K,K2,E
Q300
LPF
µ-com
Fig. 6 Transmitter PLL
Top view
(MHz)
VCO A : 450~480 (K)
480~512 (K2)
440~470 (E)
VCO B : 400~430 (K3)
VCO A : 440~460 (K,E)
480~500 (K2)
400~420 (K3)
–44.850
VCO B : 460~480 (K,E)
500~512 (K2)
420~430 (K3)
–44.850
TX-RX unit
Q355
VCO A AMP
MO
MO
Q351 : K3
VCO B
MO
IC300 Q302
PLL-IC AMP
CP,DP
EPT,LDT
IC604
MO
X3
VCXO