Kenwood TK-5810 Service Manual page 28

TK-5810 BG
(
FINAL UNIT (X45-380)
IC1
TX
(CN1)
4-6. Automatic Power Control Circuit
The automatic power control (APC) circuit stabilizes the
transmitter output power at a predetermined level and con-
sists of forward/refl ected power detector circuits.
The forward/refl ected power detector circuits detect for-
ward RF power and refl ected RF power to DC voltage, and
consists of a CM coupling type detection circuit formed by a
CM coupler.
The voltage comparator compares the voltage obtained
by the above detected voltage with the PC voltage.
An APC voltage proportional to the difference between
the sensed voltage and the reference voltage appears at the
output of the comparator. This output voltage controls the
gate voltage to the fi nal amplifi er.
4-7. Temperature Protection Circuit: TK-5810(BG)
To prevent thermal destruction of the power module (IC2),
this circuit reduces APC voltage when temperature of the
power module (IC2) rises.
The ASIC (IC708) detects temperature with a thermistor
(TH1 and TH4) and controls reference voltage to the APC
circuit.
4-8. Temperature Protection Circuit: TK-5810H(BG)
To prevent thermal destruction of the power module (IC1)
and fi nal amplifi er (Q1 and Q2), this circuit reduces APC volt-
age when temperature of the power module (IC1) and fi nal
amplifi er (Q1 and Q2) rises.
The ASIC (IC708) detects temperature with the thermis-
tor (TH1 and TH3) and controls reference voltage to the APC
circuit.
5. PLL Frequency Synthesizer
The PLL Frequency Synthesizer consists of the following
components:
• VCXO (X400)
• VCO (Q413, Q414 and Q415)
• Potentiometer IC (IC401)
• PLL IC (IC400)
• Local switch (D419 and D420)
28
/5810H BG
) ( )
CIRCUIT DESCRIPTION
Final AMP
Q1
+B
Final AMP
Q2
POWER
MODULE
Fig. 10 Final amplifi er circuit: TK-5810H(BG)
+B
CM
COUPLER
+B
D2
FWD
DET
8T
VR1
IC2
APC
PC
This PLL system is composed of a PLL IC (IC400), a crys-
tal oscillator (X400), VCO and a potentiometer IC (IC401).
VCO (Voltage Controlled Oscillator) is provided with 2
input terminals which are controlled by the potentiometer IC
and the PLL IC. The potentiometer IC brings the oscillation
frequency of VCO close to the target frequency, after the
PLL locks it up.
The operation frequency of PLL is from 450 to 520MHz
(K)/ 400 to 470MHz (K2) in TX mode and from 400.05 to
470.05MHz (K)/ 350.05 to 420.05MHz (K2) in RX mode. The
frequency steps of the PLL is 2.5, 5, 10, 12.5, 20 or 25kHz.
The comparative frequency of PLL which is 5, 10, 12.5, 20
or 25 are made by a programmable reference divider in PLL
IC (IC400) from the 16.8MHz reference signal of the crystal
oscillator (X400). Similarly, the VCO output signal is divided
into comparative frequency by the programmable N divider
in the PLL IC (IC400), and is compared with the divided ref-
erence signal in its phase detector.
The output signal of the phase detector is sent to one of
the input terminals of the VCO.
5-1. VCXO (X400)
VCXO (X400) generates a reference frequency of 16.8
MHz for the PLL frequency synthesizer. This reference fre-
quency is applied to pin 10 of the PLL IC (IC400).
The VCXO oscillation frequency is fi ne-adjusted by con-
trolling the voltage applied to pin 1 of the VCXO with the
ASIC (IC708). It is also controlled with pin 1 of the VCXO if
the output from VCXO is modulated.
5-2. VCO
There is two RX VCOs (RX VCO1, RX VCO2) and a TX
VCO.
The RX VCO1 (Q415) and RX VCO2 (Q414) generate a
1st local receive signal. The RX VCO1 oscillation frequency
is 400.05 to 435.045MHz (K), 350.05 to 385.045MHz (K2)
and the RX VCO2 oscillation frequency is 435.05 to 475.05
MHz (K), 385.05 to 420.05MHz (K2).
The TX VCO (Q413) generates a transmit carrier. The
TX VCO oscillation frequency is 450 to 520MHz (K), 400 to
470MHz (K2).
LPF
D3
REFL ANT
DET SW
D5,D6,
D7,D8,
8T
D15,D16
ANT