Kenwood TK-3230 Service Manual page 7

■ IF Amplifi er
The IF circuit is integrated in the FM IC (IC200). The IF
IC contains local input, mixer, limiter amplifi er, FM DET, and
low-frequency amplifi er.
The IF signal coming from the IF amplifi er (Q201) goes
to the IF IC mixer and is mixed with the second local signal
(38.4MHz) to produce a second IF signal. (38.85MHz –
38.4MHz = 450kHz)
The tripled PLL reference oscillation (12.8MHz x 3) is
used for the second local signal.
The second IF signal passes through ceramic filter
(CF200) to remove unwanted signals.
The second IF signal passing through the ceramic
filter passes through the limiter amplifier consisting six
differential amplifi ers and is detected.
The amplified second IF signal is demodulated by the
quadrature detector with the ceramic discriminator (CD200).
The demodulated signal is routed to the audio circuit.
■ Squelch Circuit
A squelch circuit is provided to prevent no-signal
noise or weak signals from outputting to a speaker during
transmission.
■ AF Circuit
The FM IC output passes through the base band IC
(IC300). The signal then goes through an AF volume
control, and is routed to an audio power amplifi er (IC303)
where it is amplfi ed and output to speaker. This IC have BTL
amplifier function. At internal speaker, BTL amplified. At
external speaker, IC switch off the 1 channel amplifi er by
connectors information.
SP AMP BUSY
52 76
IC403
BEEP
RSSI
MCU
12 75
Q201
38.85
MIX
MHz
16
1st IF
MIXIN
IF amp
38.4MHz
X1 Q202
12.8MHz
TCXO X3
PLL
IC303
Amp
INT. SP
Amp
J300
SW
EXT. SP
Fig. 4 IF amplifi er, Squuelch and AF circuits
CIRCUIT DESCRIPTION
IC200
DET
9
AFOUT
Amp
10
Q200
CD200
CF200
SW
450kHz
AF
W/N
IC300
HPF LPF Amp
RXAF 23
RXIN
Q301
VR301
AF VR
Narrow and wide setting can be made for each channel
by switching the demodulation level. The WIDE (low level)
and NARROW (high level) data is output from IC403, pin
69. When a Wide (low level) data is received, Q200 turn on.
When a NARROW (high level) data is received, Q200 turn
off.
Q200 turns off/on with the wide/narrow data and the
IC200 detector output level is switched to maintained a
constant output level during wide or narrow signals.
Transmitter System
■ Microphone Amplifi er Circuit
The audio signal from the microphone passes through
the MIC amplifier (IC302). Then, the signal goes through
the base band IC (IC300) that has the 6dB/oct pre-emphasis
circuit, band-pass fi lter (300 to 3kHz), amplifi er, and limiter.
The distortion components outside the audio band are
removed by the splatter fi lter.
■ Modulation Circuit
The MIC amplifi er (IC302) output passes through VR300
for modulation adjustment and goes to the modulation input
of the VCO circuit for variable reactance phase modulation.
■ Transmission Output Circuit
The VCO output is amplified by a high-frequency
amplifi er (Q101, Q103 and Q104), passes through a high-
frequency antenna switch, passes through a low-pass fi lter
and goes to the antenna.
The transmission output is about 1.5W with 3.8V DC
supply at battery terminal.
■ Low-Pass Filter Circuit
A three-stage Chebyshev type low-pass fi lter is located
between the antenna and transmit/receive switching
circuit. It removes harmonic components contained in the
transmission output.
MIC AMP VCO
MIC IC302 VR300 Q2,Q5
DRIVE FINAL
AMP AMP
Q103
Q104
Fig. 5 Transmitter section confi guration
Q303 D303 D301
MIC
SW DET
MUTE
IC302
MIC
MIC amp
Fig. 6 Microphone amplifi er circuit
TK-3230
PRE-DRIVE
RF AMP
AMP
Q6 Q101
ANT
ANT SW
D101,D200,
D201 LPF
IC300
Amp IDC LPF
7