TK-8302/8302H
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.
Narrow
IC702
pin 98
IF_IN
MIX_O
IC500
FM IC System
CF501
(Narrow)
CF500
(Wide)
R505
R507
R506
R504
D500
D501
Wide
IC702
pin 99
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.
Baseband
IC
IC701
AF PA
IC705
SP
FM IC
IC500
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.
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
RSSI
IC702
MCU
IC500
FM IC
SQIN
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 low-pass 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.
DRIVE
AMP
RF POWER
module
Q300
IC301
DC
AMP
IC501
ANT
SW
D302~D305
LPF
ANT
IC300
APC
control
Coupler
circuit
D719
APCC
IC701
pin 32
Fig. 7 APC circuit
Fig. 6 Transmitter system
ANT
IC700
MIC
MIC
AMP
D711,Q705
SW
MCU
Q6
TX
VCO
Q9
BUFF
AMP
Q10
RF
AMP
DRIVE
AMP
Q300
IC301
RF POWER
module
PLL IC
TCXO
19.2MHz
MIC key
input
IC701
Baseband
IC
IC702
X1
IC1
RF
AMP
Q3
CIRCUIT DESCRIPTION