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4 - 2
• RF signals WFM band
The WFM band signals are applied to the RF amplifier
(Q201) via the tunable band-pass filter (D202). The ampli-
fied signals pass through the tunable bandpass filter (D203),
and are then applied to the 1st mixer circuit (IC601, pin 1).
Varactor diodes (D106, D107, D202, D203, D306, D309,
D310) are employed by the tunable bandpass filter to tune
the center frequency of the bandpass filter. These diodes
are controlled by the PLL lock voltage and obtain good
image response rejection.
4-1-5 440 MHz BAND RF CIRCUIT (RF UNIT)
The signals from the antenna switching circuit (D402 and
D403) are amplified at the RF amplifier (Q401). The ampli-
fied signals pass through the bandpass filter (FI401), and
are then applied to the 1st mixer circuit (IC601, pin 1) after
being amplified at another RF amplifier (IC501).
4-1-6 1200 MHz BAND RF CIRCUIT (RF UNIT)
The signals from the antenna switching circuit (D51 and
D52) are amplified at the RF amplifier (Q51). The amplified
signals pass through the bandpass filter (FI51), and are then
applied to the RF amplifier (IC51). The amplified signal is
applied to the 1st mixer circuit (IC601, pin 1) via the band-
pass filter (FI52).
4-1-7 1ST MIXER CIRCUIT (RF UNIT)
The 1st mixer circuit converts the received RF signals into a
fixed frequency of the 1st IF signal with a 1st LO output fre-
quency. By changing the PLL frequency, only the desired
frequency will pass through at the next stage of the 1st
mixer. 1st mixer circuit produces the different 1st IF signal
for WFM and other band signals.
• 50, 144, 440 and 1200 MHz band
The applied RF signals are mixed with 1st LO signals at the
1st mixer (IC601) to produce a 69.45 MHz 1st IF signal. The
1st IF signal is output from the 1st mixer (IC601, pin 6), and
then passed through the crystal bandpass filter (FI601) to
suppress unwanted harmonic components. The filtered 1st
IF signal is applied to the IF amplifier (IC701). The amplified
signal is applied to the 2nd mixer circuit (LOGIC unit; IC701,
pin 16).
• WFM band
The RF signals are mixed with 1st LO signals at the 1st
mixer (IC601) to produce a 13.35 MHz 1st IF signal. The 1st
IF signal is output from the 1st mixer (IC601, pin 6), and then
passed through the 1st IF filter (FI602) to suppress unwant-
ed harmonic components. The filtered signal is applied to
the 2nd mixer circuit (LOGIC unit; IC701, pin 16).
The 1st LO signals are gererated at the VCO circuit which
consists of Q301, Q302, D301, Q311, Q312, D302, D311 for
50 MHz, 144 MHz and WFM, Q321, Q322, D321, D322 for
440 MHz, Q350, D351, D352 for 1200 MHz on the VCO unit.
• The 1st LO signal for 50, 144, 440, WFM band
The 1st LO signals which are generated on the VCO unit are
applied to the buffer-amplifier (Q313 and D312 for 50 MHz,
144 MHz and WFM, Q323 for 440 MHz). The buffer-ampli-
fied signals are applied to the LO-amplifier (Q822 for 50
MHz, 144 MHz and WFM, Q823 for 440 MHz), and are then
applied to the 1st mixer circuit via the TX/RX switch (D802
and D803 for 50 MHz, 144 MHz and WFM, D804 and D805
for 440 MHz) on the RF unit.
• The 1st LO signal for 1200 MHz band
The 1st LO signals which are generated on the VCO unit are
applied to the buffer-amplifier (Q351). The buffer-amplified
signals are applied to the doubler circuit (Q353), and pass-
es through the high-pass and low-pass filter. The filtered sig-
nals are applied to the 1st mixer circuit (Q601) on the LOGIC
unit after being amplified at the LO-amplifier (Q824).
• 2nd IF AND DEMODULATOR CIRCUITS (LOGIC unit)
Mixer
16
Limiter
amp.
2nd IF filter
450 kHz
RSSI
IC701 TA31136FN
13
2nd IF (19.65 MHz)
from Q701 (RF unit)
"SD" signal to the CPU
pin 3
11
10
9
8
7
5
3
2
Active
filter
FI701
Noise
detector
FM
detector
Noise
comp.
"NOISE" signal to the CPU
pin 12
12
R729
C712
C720
C733
C734
C736
R731
R58
R730
WFM
AF signal to AF filter
(LOGIC unit; IC241)
2nd
Q702
"2nd LO" signal from
IC801, pin 13 (RF unit)
C733
R735
R706
R727
C701