Icom IC-775 Service Manual

4-6
DSP
CIRCUITS
The DSP
(Digital
Signal
Processor)
unit enables
digital
noise
reduction,
digital PSN
(Phase Shift
Network) modu-
lation/demodulation,
digital AF
automatic notch,
digital LPF
and HPF,
ultra-narrow
CW filter
and digital
automatic APF
(Audio
Peak
Filter).
4-6-1
DSP
RECEIVING
(DSP
UNIT,
IC-775DSP
only)
When
receiving with
the DSP
function
ON, detected AF
signals are
applied
to the DSP
unit via the AF
selector (IF
unit IC17).
When
receiving with PSN
demodulation
in
SSB/
CW/RTTY
modes,
the
product detector
(IF unit IC14) func-
tions
as a 5th
mixer to
obtain a 15
kHz IF signal.
The IF
signal is
applied to the
DSP unit (J1
pin
8)
via
IC17
(IF unit)
instead of
AF
signals.
The AF
or IF
signals
pass through the
analog switch (IC3
pins
1,15)
and are
applied
to the A/D
converter (IC8).
The
digital
signal is
demodulated (5th IF
signal) by
the PSN
method at IC14
and
digitally
manipulated at IC15.
The
resulting
digital
signal is then
converted into an
analog
signal at
the D/A
converter (IC9).
The
converted signal
passes through
the
limiter-amplifier
(IClOa)
and an analog switch (IC3
pins
13, 14).
The
signal
is
amplified at
the
limiter-amplifier (IC4a),
passes
through
the
active low-pass
filters (IC5a,
IC5b) and is then
applied
to the
switched
capacitor
filters (IC6, IC7).
The cut-off
frequencies of IC6
and IC7
can be
programmed. The
resulting
signal passes
through IClOb
and IC3 (pins
3, 4)
and is
applied to
the AF
selector (IC16) in the IF
unit.
4-6-2
DSP
TRANSMITTING
(DSP UNIT,
IC-775DSP
only)
When
transmitting with the
DSP
function
ON,
microphone
signals are
applied to the DSP
unit
(J1
pin
4)
via the AF
selector
(IF unit
109).
The AF
signals
pass through
the analog switch (IC3
pins
12, 14),
the
limiter-amplifier (IC4a),
the
active low-pass
filters
(IC5a, IC5b)
and are then
applied to the switched
capacitor
filters (IC6, IC7).
The
cut-off frequencies of IC6
and IC7
can be
programmed. The
resulting AF
signal
passes
through IC1
Ob and IC3
(pins
4/5,
2/1
5)
and is then
converted into a
digital signal at
the A/D converter (IC8).
The
digital signal is
modulated by the PSN
method at IC1
4
and
digitally
manipulated at 1015.
The resulting digital
signal is
then converted into
an analog signal at the D/A
converter
(109).
The
converted
signal passes
through the
limiter-amplifier
(1010a),
filtered at the
active high-pass filter
(1011),
ampli-
fied at 104b
and is
applied to the AF selector
(109)
in the IF
unit.
4-13

Icom IC-775 Specifications

General

Brand	Icom
Model	IC-775
Category	Transceiver
Language	English