Kenwood TH-F6A Service Manual page 13

MIC
7-2. Transmission circuit
For the VHF VCO output, the 500MHz output passes through
the RF amplifier (Q13), is divided into 1/4 and amplified by
Q19. The signal passes through switch D101/D102, is amplified
by four amplifiers Q71, Q72, Q54, and Q56, and amplified to
the final output by power amplifier Q55. The signal passes
through a low-pass filter, an antenna switch, and another low-
pass filter, and is sent to the antenna.
[(K only) The 220MHz VCO output is produced by passing
the 400MHz output through the RF amplifier (Q13), dividing it
into 1/2 by IC3, and amplifying it by Q19. The signal passes
through a switch (D101/D102), is amplified by four amplifiers
Q71/Q72/Q54/Q56, and amplified to the final output by power
amplifier Q57. The signal passes through a low-pass filter, an
antenna switch, and another low-pass filter, and is supplied
to the antenna.]
VCO
B
AMP AMP
Q9MT6C03AE
Q13
Q12
D18 HVC131
2SC
D11,12
2SC
HVC3758 5108(Y)
5009
D21 HVC131
D10,16
HVC3758
UHF
DEVIDER
IC3
VHF
UPB
1509GV
7-3. APC circuit
The APC circuit is used to provide stable transmission
output, detects drain current of the power module and controls
transmission output. The voltage produced at R204, and R206
is amplified by IC8 and Q50, and the difference between the
voltage and the reference voltage of each band/power output
from the CPU (IC705) is detected by IC9 to produce APC
voltage. This voltage controls the gain of Q54, Q56, Q55, and
Q57.
CIRCUIT DESCRIPTION
SW
IC703
TC7S66FU
MUTE SW MIC AMP
Q707 IC702
25J NJM
347 2102F
AGC
LIMITTER
Q726
2SC4919
D710
D705
D711
RB706F-40
DA221
D718
DAN222
SW SW
AMP AMP
Q21 D99 D102 Q71
2SC HSC HSC 2SC4226
5009 277 277 (R24)
AMP
Q93 D100
MT6C HSC
03AE 277
AMP
Q19 D101
2SC HSC
5009 277
TONE & 96H AMP
DTMF
VOX PRE-EMPHASIS
Q701
IC701
2SC4617
TA75W
D709
558FU
RB706F-40
AF AMP
VOXIN
Fig.19
The UHF VCO output is directly produced, passes through
RF amplifier Q13, and is amplified by Q93. It passes through
switch D100/D102, is amplified by four amplifiers Q71/Q72/
Q54/Q56, and amplified to the final output by power amplifier
Q55. It passes through a high-pass filter, an antenna switch,
and an antenna filter, and goes to the antenna.
AMP DRIVE AMP DRIVE AMP RF POWER AMP
Q72 Q54 Q56 Q55
2SC 2SK 2SK 2SK
5192 2973 2973 3476
Fig.20
7-4. Temperature protection circuit
To prevent thermal destruction of the final power amplifier,
the voltage of the thermistor TH1 installed near the power
module is monitored by the CPU IC705. If the prescribed
temperature is exceeded, the APC voltage is decreased to
reduce heat generation.
TH-F6A/F7E
IC719
VCO
IC706
M62364
B
FP
Q9MT6C03AE
D18 HVC131
D11,12
HVC3758
D21 HVC131
D10,16
HVC3758
X1
IC720 TCX0
L77-1859-05
HPF SW HPF LPF
D53
UHF
D54
HVC131
LPF SW
LPF
D49 D85
D50 D86
D51
VHF
D52
HVC131
BPF
ANT
13