4 - 3
4-1-7 3RD MIXER CIRCUIT
The 3rd mixer circuit mixes the 2nd IF signal and 3rd LO sig-
nal to produce a 450 kHz 3rd IF signal (except WFM mode).
The 10.7 MHz 2nd IF signal from the IF amplifier (Q29) is
applied to the 3rd mixer section in the FM IF IC (IC10, pin
16). The applied signal is mixed with a 3rd LO signal gener-
ated by X1 (10.25 MHz) to produce a 450 kHz 3rd IF signal.
The 3rd IF signal is output from pin 3, and passed through
one of 2 bandpass filters (FI6 or FI7) or bypassed, accord-
ing to the selected mode after being amplified at the IF
amplifier (Q38). The filtered or bypassed signal is applied to
the each demodulator circuit (except WFM mode).
• Bandpass filter selection
4-1-8 DEMODULATOR CIRCUITS
The demodulator circuit converts the 2nd IF signal into AF
signals. 3 separate demodulator circuits are employed for
each mode.
(1) WFM mode
The 10.7 MHz 2nd IF signal from the IF amplifier (Q29) is
applied to the WFM demodulator circuit (IC7, pin 1).
The IF signal is applied to the quadrature detector section
(IC7, pin 11) to demodulate AF signals. The demodulated AF
signals are output from pin 14, 15, and are then applied to
the AF switch circuit.
(2) FM mode
The filtered or bypassed 3rd IF signal is applied to the quad-
rature detector section in the FM IF IC (IC10, pin 10) then
mixed with the signal generated by the discriminator (X2) to
demodulate AF signals. The AF signals are output from pin
9 and applied to the AF switch circuit via the high-pass filter
circuit (IC11).
(3) AM mode
The filtered 3rd IF signal from the one of 2 bandpass filters
(FI6 or FI7) is amplified at the IF and buffer amplifiers (Q42,
Q43). The amplified IF signal is applied to the AM detector
circuit (D63) to be converted into AF signals, and the AF sig-
nals are applied to the AF switch circuit.
4-1-9 AF SWITCH CIRCUIT
The demodulated AF signals from the demodulator circuits
are applied to the AF switch (IC14). This consists of 4 ana-
log switches which are selected with a mode signal from the
CPU (IC21) via the I/O expander (IC3). The switched AF sig-
nals are applied to the AF circuit.
4-1-10 AF CIRCUIT
The AF signals from the AF switch circuit are passed
through the AF mute switch and then amplified at the AF
power amplifier circuit.
The AF signals from the AF switch are applied to the elec-
tronic volume control circuit (IC23, pin 1). The level con-
trolled AF signals are output from pin 2 and applied to the AF
power amplifier (IC25, pin 6). The power amplified AF sig-
nals are applied to the internal speaker via the [EXT SP]
jack.
The electronic volume control circuit controls AF gain, there-
fore, the AF output level varies according to the [VOL] set-
ting and also the squelch conditions.
4-1-11 SQUELCH CIRCUIT
A squelch circuit cuts out AF signals when no RF signal is
received or when the S-meter signal is lower than the
[SQUELCH] control setting level. By detecting noise compo-
nents in the AF signals, the CPU controls the electronic vol-
ume control circuit.
• NOISE SQUELCH
Some noise components in the AF signals from pin 9 of the
FM IF IC (IC10) are applied to the noise amplifier section in
the IC (IC10, pin 8). The amplified signals are output from
pin 7. The output signals are applied to the noise and buffer
amplifiers (Q58, Q59) and rectified at the noise detector
(D89) to be converted into DC voltage, then applied to the
CPU (IC21, pin 60) as an NOIN signal.
Modes
Bandpass filter
Passband width
AM
FI6
6 kHz
FM
FI7
15 kHz
IC9
IC10
AFFM
AWFL
AWFR
AFAM
IC14
IC29
11
10
8
1
7
2
12
9
8
6
4
3
5
1
7
2
13
D63
• Squelch and AF amplifier circuits
FM
Detector
WFM
Detector
AM
Detector
FM5
WFM5
WFM5
AM5
AF power
Amplifier
AF switch
IC23
Electronic
volume
SP
7
6
1
3
IC25
J7
External SP jack