Kenwood TK-7302 Service Manual page 11

2-4. Wide/Narrow Switching Circuit
The Wide port (pin 99) and Narrow port (pin 98) of the
MCU is used to switch between ceramic fi lters. When the
Wide port is high, the ceramic fi lter switch diodes (D500,
D501) cause CF500 to turn on to receive a Wide signal.
When the Narrow port is high, the ceramic fi lter switch
diodes (D500, D501) cause CF501 to turn on to receive a
Narrow signal.
IC500
FM IC System
IF_IN
CF500
(Wide)
CF501
(Narrow)
D500
Narrow
IC702
pin98
Fig. 3 Wide/Narrow switching circuit
2-5. AF Signal System
The detection signal from the FM IC (IC500) goes to the
baseband IC (IC701) DISC input (pin 16) for characterizing
the signal.
The AF signal output from IC701 is input to the audio
power amplifi er (IC705). The AF signal from IC705 switches
between the internal speaker and the speaker jack (J701)
output.
IC500 IC701
Baseband
FM IC
IC
Fig. 4 AF signal system
2-6. Squelch Circuit
The detection output from the FM IC (IC500), a voltage
is applied to the MCU (IC702). The MCU controls squelch
according to the voltage (SQIN) level.
The signal from the RSSI pin of IC500 is monitored.
MIC IC700 D711,Q705
MIC
SW
AMP
MIC key
input
CIRCUIT DESCRIPTION
MIX_O
R504
Wide
IC702
pin99
R506
D501
IC700 SP
AF PA
IC701
Baseband
IC
TCXO
MCU
19.2MHz
IC702 X1
Fig. 6 Transmitter system
TK-7302/7302
The electric fi eld strength of the receive signal can be
known before the SQIN voltage is input to the MCU, and
the scan stop speed is improved.
N-REC
IC500
FM IC
RSSI
Fig. 5 Squelch circuit
3. Transmitter System
3-1. Outline
The transmitter circuit produces and amplifies the de-
sired frequency directly. It FM-modulates the carrier signal
by means of a varicap diode.
3-2. Power Amplifi er Circuit
The transmit output signal from the VCO passes through
the transmission/reception selection diode (D719) and am-
plifi ed by Q300. The amplifi ed signal goes to the RF power
module (IC301) through a low-pass fi lter. The lowpass fi lter
removes unwanted high-frequency harmonic components,
and the resulting signal goes through the antenna terminal.
3-3. APC Circuit
The automatic transmission power control (APC) circuit
detects part of a fi nal amplifi er output with a coupler circuit
and applies a voltage to IC300. IC300 compares the APC
control voltage (PC) generated by the baseband IC (IC701)
and DC amplifi er (IC501) with the detection output voltage.
IC300 generates the voltage to control IC301 and stabilizes
transmission output.
The APC circuit is confi gured to protect over current of
Q300 and IC301 due to fl uctuations of the load at the anten-
na end and to stabilize transmission output at voltage and
temperature variations.
Q300 IC301
DRIVE RF POWER
D719
AMP module
APCC
DC APC
IC701
AMP control
pin 32
IC501 IC300
Fig. 7 APC circuit
Q6 Q9 Q10
BUFF RF
TX
VCO AMP AMP
RF
PLL IC
AMP
IC1 Q3
V /7302H/7302H
( )
SQIN
IC702
MCU
RSSI
D302~D305
ANT
LPF
SW
Coupler
circuit
ANT
Q300 IC301
DRIVE
RF POWER
AMP module
V
( )
ANT
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