Kenwood TK-3000 Service Manual page 8

TK-3000
2-3. IF Amplifier Circuit
The first IF signal is passed through a four-pole mono-
lithic crystal filter (XF200) to remove the adjacent channel
signal.
The filtered first IF signal is amplified by the first IF ampli-
fier (Q202) and then applied to the lF system IC (IC200).
The IF system IC provides a second mixer, second local
oscillator, limiting amplifier, quadrature detector and RSSI
(Received Signal Strength Indicator).The second mixer
mixes the first IF signal with the 38.4MHz of the second lo-
cal oscillator output (TCXO X1) and produces the second IF
signal of 450kHz.
The second IF signal is passed through the ceramic filter
(CF200) to remove the adjacent channel signal. The filtered
second IF signal is amplified by the limiting amplifier and
demodulated by the quadrature detector with the ceramic
discriminator (CD201).The demodulated signal is routed to
the audio circuit.
2-4. Audio Amplifier Circuit
The demodulated signal from IC200 is amplified by
IC305, IC303 and goes to AF amplifier through IC302.
The signal then goes through an volume control (VR500),
and is routed to an audio power amplifier (IC302) where it is
amplified and output to the speaker.
To output sounds from the speaker, IC400 sends a high
signal to the SPMUT line and turns IC400 on through Q300,
Q301, Q302 and Q306.
8
CIRCUIT DESCRIPTION
Q100
From
Pre-DRIVE
T/R SW
AMP
(D100)
R121
+B
R122
R123
CURDET
Fig. 4 Drive and final amplifier circuit
3. Transmitter System
3-1. Microphone Amplifier Circuit
The signal from microphone amplified by IC301 and goes
through mute switch (IC300).
IC304 is composed of high-pass filter, low-pass filter and
pre-emphasis/IDC circuit.
The output signal from the DAC IC (IC300) goes to the
VCO modulation input.
MIC
BUFF
MIC
AMP
IC304
Fig. 3 Microphone amplifier circuit
3-2. Driver and Final Amplifier Circuit
The signal from the T/R switch (D100 is on) is amplified
by the pre-drive amplifier (Q100) to 30mW.
The output of the pre-drive amplifier is amplified by the
drive amplifier (Q101) and the RF final amplifier (Q102) to
4.0W (1W when the power is low).
The drive amplifier and the RF final amplifier consist of
two MOS FET stages.
The output of the RF final amplifier is then passed
through the harmonic filter (LPF) and antenna switch (D101
and D102) and is applied to the antenna terminal.
Q101 Q102 D101,102
DRIVE RF FINAL
AMP AMP
VG
VDD
POWC
IC300
IC301
DAC
TCXO
LSDO
LSDO
ANT
ANT
LPF
SW
VCO
X1