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4-2 AF CIRCUITS (LOGIC UNIT)

FM mode

The demodulated AF signal is passed through the
de-emphasis circuit (R323 and C316) and AF filter (Q301),
and then applied to the AF AMP (Q300) through the AF line
SW (D300).

Wide FM/AM mode

The demodulated AF signal is passed through the AF filter
(R316, R320 and C314) and the AF line SW (Q302), and
then applied to the AF AMP (Q300).

The amplified AF signal is passed through the LPF (R350
and C404), whose frequency response is changed by Q508
according to the user setting (The "AF FILTER"). The filtered
AF signal is passed through the AF mute SW (Q350), and
then adjusted in level by the electric VR (IC451).

The level-adjusted AF signal is applied to the AF power
AMP (IC450).

AUDIO POWER AMPLIFIER

IC450 is a BTL (Bridge-Tied Load) audio power amplifier
which provides high AF output power.

The amplified AF signal is passed through the speaker mute
SW (Q507), and then applied to the internal or external
speaker.

• AF CIRCUITS

4 - 3

AF
AMP

MUTE

AF
AMP

SP1

LOGIC UNIT

WFM/AM

FILTER

MODE

M ODE

Electric

From the demodulator circuits

IC450

IC451

Q350

Q300

D300

Q301

Q302

SP1(CHASSIS)

EXT SP

LPF

CTRL

Q508

SPEAKER

Q507,D505

MUTE

4-3 FREQUENCY SYNTHESIZER CIRCUITS

(RF UNIT)

1st VCO

The 1st VCO is composed of Q528, Q529 and D105,
and generates the 1st LO signal, ranging from 266.8 to
550 MHz. This VCO has a shift switch which changes the
oscillating frequency range. The output signal is amplified
by Q525, and then applied to both the buffer (Q43) and the
doubler circuit.

DOUBLER CIRCUITS FOR THE 1ST LO SIGNAL

IC-R6 has two doubler circuits, "DBL1" and "DBL2". They
double the frequency of the VCO output signal to obtain the
1st LO signal with a wide frequency range.

The "DBL1 (Q31, D43 and D50)" doubles the VCO output
signal ranging from 274.85 to 400 MHz, and the "DBL2 (Q31,
D44 and D47)" doubles the signal ranging from 380.45 to
549.85 MHz. When the fundamental frequency signal is
directly used as the 1st LO signal, the VCO output signal
by-passes both doubler circuits through D42 and D52.

2nd VCO

The 2nd VCO is composed of Q6, D17, L45, C80, C207
and C208, and generates 247.05/286.35 MHz (for FM and
AM modes) and 246.750/286.650 MHz (for WFM mode) 2nd
LO signals.

PLL (Phase Locked Loop) CIRCUIT

A portion of signal from each VCO is fed back to the PLL IC
(IC3). The output signal of the 1st VCO is applied to pin 11
of the IC, through the buffer (Q43), and that of the 2nd VCO
is applied to pin 19.

The applied VCO output signal is divided and phase-
compared with a 19.2 MHz reference frequency signal from
the TCXO (X1), which is also divided. The resulting signal of
the phase comparison is output from pin 5 (to the 1st VCO)
or pin 2 (to the 2nd VCO) through the internal charge pump,
and DC-converted by the loop fi lter, and then applied to the
VCO as the lock voltage.

When the oscillation frequency drifts, its phase changes from
that of the reference frequency, causing a lock voltage change
to compensate for the drift in the VCO oscillating frequency.

• FREQUENCY SYNTHESIZER CIRCUITS

BUFF

PLL IC

Prescaler

Phase

comparator

Charge

pump

Divider

Prescaler

Phase

comparator