User's Manual

PRELIMINARY

PRELIMINARY PRELIMINARY

PRELIMINARY –

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Service

ServiceService

Service Manual

Manual Manual

Manual

DR• CHKD• APPD•

Fig. 2. Receiver section configuration

）

First Mixer

The signal from the RF amplifier is heterodyned with the first local

oscillator signal from the PLL frequency synthesizer circuit at the first

mixer (Q202) to create a 38.85 MHz first intermediate frequency (1

IF) signal. The first IF signal is then fed through two monolithic crystal

filters (MCFs: XF200) to further remove spurious signals.

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IF amplifier

The first IF signal is amplified by Q201, and then enters IC 200 (FM processing IC). The

signal is heterodyned again with a second local oscillator signal within IC200 to create a

450kHz second IF signal. The second IF signal is then fed through a 450kHz ceramic filter

(CF200) to further eliminate unwanted signals before it is amplified and FM detected in

IC200.

4） AF amplifier

The recovered AF signal obtained from IC200 is amplified by IC300

(1/4), filtered by the IC300 low-pass filter (2/4) and IC300 high-pass

filter (3/4) and (4/4), and de-emphasized by R303 and C306. The AF

signal is then passed through a WIDE/NARROW switch (Q303). The

processed AF signal passes through an AF volume control and is

amplified to a sufficient level to drive a loud speaker by an AF

power amplifier (IC302).

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Squelch

Part of the AF signal from the IC enters the FM IC again, and the

noise component is amplified and rectified by a filter and an

amplifier to produce a DC voltage corresponding to the noise level.

The DC signal from the FM IC goes to the analog port of the

microprocessor (IC403). IC403 determines whether to output

sounds from the speaker, IC403 sends a high signal to the MUTE and

AFCO lines and turns IC302 on through Q302, Q304, Q305, Q306

and Q307. (See Fig.3)