Fm/Am Demodulator Circuits; Digital (Dv) Demodulator Circuits; Af Filter Circuits; Af Power Amplifier - Icom ID-880H Service Manual

FM DEMODULATOR CIRCUITS
In the FM mode, the filtered 2nd IF signal input from
pin 7 is amplified by the internal limiter amplifier, and FM-
demodulated at the internal quadrature detector. The
demodulated AF signals are then output from pin 11 and
applied to the AF circuits via the AF switch (IC13).
AM DEMODULATOR CIRCUITS
In the AM mode, the filtered 2nd IF signal input from
pin 5 is amplified by the internal limiter amplifier, and AM-
demodulated at the internal AM detector. The demodulated
AF signals are output from pin 14 and applied to the AF fi lter
circuits via the AF switch (IC13).

DIGITAL (DV) DEMODULATOR CIRCUITS

In the DV mode, the filtered 2nd IF signal input from
pin 7 is amplified by the internal limiter amplifier, and
FM-demodulated at the internal quadrature detector.
The demodulated AF signals are applied to the digital
demodulator circuits via the AF switch (IC13).
The FM-demodulated AF signals from the AF switch (IC13)
are applied to the modem (IC1012) via the two buffers (IC49b;
pins 6, 7 and IC1014), and converted into the digital signal.
The converted digital signal is applied to the DSP CODEC
(IC1) via the level converter (IC1000, 1001, 1002), to be
decoded into the AMBE signal. The decoded AMBE signal is
then applied to the liner CODEC IC (IC1006) to be converted
into the analog audio signal. The converted AF signals are
applied to the RX AF circuits.
• DIGITAL (DV) DEMODULATOR CIRCUITS
IC49b
IC1014
From the FM demodulator
circuits (DV mode)
BUFF BUFF
IC1000,1001,1002
LEVEL
CNV.
IC1012
MODEM
IC1013
IC1006
To the AF filter circuits
(DV mode)
DSP LINEAR
CODEC CODEC

AF FILTER CIRCUITS

The demodulated AF signals are applied to the AF filter
(Q47) via the digital/analog signal selector (IC11), to obtain
suitable audio response the for receive mode (FM, AM or
DV).
The frequency response of the fi lter is controlled by "AFFIL_
SEL" signal from the CPU (IC25).
The fi ltered AF signals are applied to the variable pass-band
frequency audio filter circuit (IC49a; pins 3, 1). The circuit
reduces audible noises included in the demodulated AF
signals.
The fi ltered AF signals are applied to the electric volume IC
(IC66) which adjusts the loudness by "AF_VOL_DATA" and
"AF_VOL_CK" signals from the CPU (IC25).
The level-adjusted AF signals are applied to the AF power
AMP (IC38) via the AF mute SW (Q102).

AF POWER AMPLIFIER

The AF signals from the AF mute SW (Q102) are applied to
the AF power AMP (IC38), and amplifi ed to obtain AF output
power. The power-amplified AF signals are applied to the
internal speaker (CHASSIS; SP1) via J8.
If an external speaker is connected to the external speaker
jack (J8), the power-amplifi ed AF signals from the AF power
AMP (IC38) are applied to the connected speaker via J8.
• AF FILTER CIRCUITS AND AF POWER AMPLIFIER
[EXTERNAL SPEAKER JACK]
Q102
IC38
SP
J8
AF
MUTE
AM P
SP1
Internal speaker
IC49a
AF
FILTER
4 - 3
IC66
Volume
control
AF_VOL_DATA
AF_VOL_CK
Q47 IC11
From the FM/AM demodulator circuits
(FM/AM mode)
AF DIGI/AN
FILTER SELECT
From the digital demodulator circuits
(DV mode)
AFFIL_SEL