TM-V708A
9
CIRCUIT DESCRIPTION
Fig. 10 APC circuit
3-3. APC circuit
The Automatic transmission Power Control (APC) circuit
has a differential amplifier (IC200) that compares the DC
voltage generated by detecting part of the transmission
output using diodes (VHF: D18, D19; UHF: D317, D318) with
DC AMP
DB
Q208
2SB1565
(E,F)
DC AMP
COMPARATOR
Q209
2SC4617
(R)
IC200
TA75S01F
D318
D317
D19
D18
VHF
UHF
CPU
the reference voltage output from the CPU. The output signal
is amplified by Q209 and Q208 and fed to the power module
to keep transmission output constant.
3-4. Overheating protection circuit
To protect from the thermal destruction of the power
module, the voltage of the thermistor (TH1) near the power
module is monitored by the CPU (IC604). If it becomes high
temperature, the APC voltage is controlled to cool down the
temperature.
4. PLL circuit
4-1. Reference oscillator circuit
The 12.8MHz signal is generated by the crystal oscillator
circuit (IC1 and IC301) and internally divided to generate 5kHz
or 6.25kHz reference frequency. The 12.8MHz signal on IC1
side is tripled by Q102 to obtain the second local oscillator for
the A band. The reference oscillation circuit is also modulated
to improve the modulation characteristics of the DCS and
9600bps packet signal when it is transmitted.
Fig. 11 PLL circuit
VHF VCO
HT
CV
Q3
2SC5108
(Y)
PLL
LD
Q102
2SC4649
(N,P)
38.4MHz
12.8MHz
X3
IC1
MB1511PFV-GBND
CHARGE PUMP
Q1 2SA1774(S)
Q2 2SC4617(R)
IC2
KCH38
UHF VCO
HT
CV
Q304
2SC5108
(Y)
PLL
12.8MHz
LD
IC301
MB1511PFV-GBND
CHARGE PUMP
Q300 2SA1774(S)
IC302
KCH28
Q301 2SC4617(R)
