TM-V708A
8
CIRCUIT DESCRIPTION
Fig. 8 Modulation circuit
Fig. 9 Transmitter circuit
3. Transmitter system
3-1. Modulation Circuit
The audio modulation input from the microphone is
amplified by IC801. The DTMF signal and 1750Hz tone signal
generated by the CPU are also mixed by IC801. The
modulation signal from the DATA terminal is switched by
IC803. It is directed to IC801 in 1200bps mode and to IC802
in 9600bps mode. The signal amplified by IC801 is pre-
emphasized by Q801 and Q802, and its level is adjusted by
IC804, and the resulting signal goes to each of the VHF and
UHF VCOs as a modulation signal. The TONE/CTCSS/DCS
signal generated by the CPU is fed to IC802 in the same way
as the 9600bps mode signal from the DATA terminal. The
signal amplified by IC802 is distributed and the level is
adjusted. The modulating signal goes to each of the VHF and
UHF VCOs. The signal is amplified by IC300 and modulates
the reference oscillation circuit.
3-2. Transmitter circuit
The VHF VCO output is amplified by 3-stage amplifier, RF
amplifier (Q6) and driver amplifier (Q8, Q9). It is amplified to
the final output by the power module. The signal passes
through antenna switch (D14, D15) and low-pass lifter and is
fed to the antenna.
The UHF VCO output is amplified by 4-stage amplifier, RF
amplifier (Q304) and driver amplifier (Q307, Q309, and Q310).
It is further amplified to the final output by the power module.
The signal passes through antenna switch (D314), low-pass
filter and high-pass filter. Then it is fed to the antenna.
VHF
VCO
UHF
VCO
AF AMP
Q802
2SC4617
(S)
PRE-EMPHASIS
MIC AMP
DTMF1750
IC801
IC804
M62364FP
Q801
2SC4617
(S)
NJM2100V
TONE/CTCSS/DCS
1200bps
SW
PKD
CPU
IC803
BU4066
BCFV
IC803
BU4066
BCFV
AMP
IC300
NJM2904V
IC2
KCH38
IC302
KCH28
IC802
TA75S01F
SW
TONE AMP
MIC
POWER AMP
LPF
HPF
Q310
2SC2954
Q309
2SC3357
Q307
2SC4093
(R27)
UHF VCO
Q304
2SC5108
(Y)
IC302
KCH28
POWER AMP
DRIVER
DRIVER
RF AMP
LPF
Q9
2SC2954
Q8
2SC3357
Q6
2SC5108
(Y)
VHF VCO
IC2
KCH38
M67746
M57788MR-24
ANT
ANT