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The 150–349.999 MHz signals from the band switching
diode (D16) pass through the high-pass filter (L27–L29,
C69–C74) and tunable bandpass filter (D18, L31–L33), and
are then amplified at the RF amplifier (Q9) and pass through
another tunable bandpass filter (D19, L35–L37). The filtered
signals are applied to the 1st mixer circuit (IC4) via the band
switching diode (D20).
The 350–699.999 MHz signals from the band switching
diode (D21) pass through the high-pass filter (L40, C92–
C94) and tunable bandpass filter (D22, D23, L41, L42). The
filtered signals are then amplified at the RF amplifier (Q10)
and pass through the tunable bandpass filters (D24, D77,
L45–L47). The filtered signals are applied to the 1st mixer
circuit (IC4) via the band switching diode (D25).
The 700–1300 MHz signals from the band switching diode
(D26) pass through the high-pass filter (L141, C110, C606)
and 2-stage tunable bandpass filters (D27, D28, L163, D29,
D30, L51–L53). The filtered signals are then amplified at the
RF amplifier (Q11) and pass through the tunable bandpass
filters (D31, D32, L56, L178). The filtered signals are applied
to the 1st mixer circuit (IC4) via the band switching diode
(D33).
The tunable bandpass filters employ varactor diodes to tune
the center frequency of the RF passband for wide bandwidth
receiving and good image response rejection. These diodes
are controlled by TUNV signal from the CPU (IC21, pin 54)
via the tune controller (IC22b).
• Tunable bandpass filters
Receive freq.
BPF select
(MHz)
signal
50.0–149.999
B4
150.0–349.999
B5
350.0–699.999
B6
700.0–1300.0
B7
• IF and demodulator circuits
1st IF signal from
Q13
1st mixer (IC4)
BPF
IF Amp.
to AF switch IC14
Varactor
diodes
D11–D14, D80–D83
D18, D19
D22–D24, D77
D27–D32
2nd Mixer
BW: 50 kHz
IC5
BW: 230 kHz
2nd LO
WFM
WFM
Detector
IC7
FM
HPF
AM
ANL
Q44, D52
4-1-5 1ST MIXER CIRCUIT
The 1st mixer circuit converts the received RF signals into a
fixed frequency of the 1st IF signal with a PLL output fre-
quency. By changing the PLL frequency, only the desired
frequency will pass through the bandpass filters at the next
stage of the 1st mixer.
The filtered RF signals are mixed with 1st LO signals at the
1st mixer circuit (IC4) to produce a 266.7 MHz 1st IF signal.
The 1st IF signal is output from pin 5, and passed through
the bandpass filter (FI1) to suppress unwanted harmonic
components. The filtered 1st IF signal is applied to the IF cir-
cuit.
The 1st LO signals are generated at the VCO 1 (Q14, Q15)
or VCO 2 (Q18, Q19) circuit (according to the receiving fre-
quency band) and are amplified at the buffer amplifier
(IC26). The amplified signals are then applied to the 1st
mixer (IC4, pin 2) directly or passed through the divider cir-
cuit (IC6).
4-1-6 1ST IF AND 2ND MIXER CIRCUITS
The 2nd mixer circuit converts the 1st IF signal into a 2nd IF
signal.
The filtered 266.7 MHz 1st IF signal from the bandpass filter
(FI1) is amplified at the 1st IF amplifier (Q13) then mixed
with the 2nd LO signal at the 2nd mixer circuit (IC5) to pro-
duce a 10.7 MHz 2nd IF signal. The 2nd IF signal is passed
through either 2 bandpass filters (FI2 or FI3; depending on
the selected mode and bandwidth). The filtered 2nd IF sig-
nal is amplified at the IF amplifier (Q29), then applied to the
RF
WFM demodulator or 3rd IF circuit.
amp.
Q8
Q9
Q10
Q11
IF Amp.
10.25 MHz
FI2
Q29
FI3
16
AM
detector
D63
4 - 2
FI7
IF Amp.
FI6
X1
Q38
1
3
5
3rd
LO
Limiter
3rd
Mixer
11
10
X2
450 kHz
Buffer Amp.
IF Amp.
Q42
Q43
7
8
Active
filter
FM
Detector
9
IC10
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