Icom IC-7000, Руководство по обслуживанию, Страница: 8 / 92

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The amplified IF signal is passed through the bandpass filter
(FI1402) and then applied to the WFM demodulator circuit
(IC1401).
3-1-8 3RD MIXER CIRCUIT (MAIN UNIT)
The 3rd mixer circuit mixes the 2nd IF signal with the 3rd LO
signal to convert into the 3rd IF frequency.
The amplified signal from the IF amplifier (Q1001) are mixed
with the 3rd LO signal (438.85 kHz), where come from the
DDS unit via J2406, at the 3rd mixer circuit (IC1101) to con-
vert into the 16.15 kHz 3rd IF signal.
The converted 3rd IF signal is applied to the 3rd IF circuit.
3-1-9 3RD IF CIRCUIT (MAIN UNIT)
The 3rd IF circuit filters and amplifies the 3rd IF signal.
The converted 3rd IF signal is amplified at the 3rd IF ampli-
fier (IC1203, pins 5, 7) and then passed through the low-
pass filter (IC1203, pins 1, 3). The filtered signal is passed
through the mode switches (IC1201, pins 1, 7; IC1202, pins
1, 7) and then applied to the analog switch (IC1256, pins 11,
13).
The switched signal is applied to the DSP circuit (LOGIC
unit) via the J2251 (pin 1).
3-1-10 DEMODULATOR CIRCUITS (MAIN UNIT)
• WFM mode
The demodulator circuit converts the 2nd IF signal into the
AF signals.
The filtered signal from the bandpass filter (FI1402) is
applied to the IF amplifier section inside the WFM demodu-
lator (IC1401, pin 1) and then applied to the quadrature
detector section to convert into AF signals. The detected AF
signals are output from pin 6 (IC1401) and then applied to
the mode switches (IC1201, pins 1, 7; IC1202, pins 1, 6).
The switched AF signals are applied to the analog switch
(IC1256, pins 11, 13) and then applied to the DSP circuit
(LOGIC unit) via J2251 (pin 1).
3-1-11 DSP CIRCUIT (LOGIC UNIT)
The DSP (Digital Signal Processor) circuit enables digital IF
filter, manual notch, digital twin PBT and phase demodula-
tion, etc.
The 3rd IF or demodulated AF (WFM mode) signals are
passed through the low-pass filter (IC451, pins 1, 2) and
then applied to the A/D converter (IC551, pin 4). The con-
verted signals are applied to the DSP ICs (IC301, IC2201)
for the digital IF filter, demodulation, automatic notch and
noise reduction, etc.
The output digital audio signals from the DSP IC (IC301) are
applied to the D/A converter (IC551) to convert into the ana-
log audio signals.
The converted audio signals from the D/A converter (IC551,
pins 25, 26) are passed through the low-pass filter (IC601,
pins 5–7), and then applied to the AF amplifier circuit (MAIN
unit) via J701 (pin 14).
3-1-12 AF AMPLIFIER CIRCUIT (MAIN UNIT)
The AF amplifier amplifies the demodulated AF signals to
drive speaker.
The filtered signal from the low-pass filter (LOGIC unit;
IC601, pins 5–7) are passed through another low-pass filter
(IC2551, pins 1, 3).
While in FM mode, the filtered AF signals from the low-pass
filter (IC2551, pin 1) are applied to the de-emphasis circuit
(IC2551, pins 5–7) to obtain the –6 dB/octave characteristics
and then applied to the AF switch (IC2601, pins 1, 6).
While except FM mode, the filtered AF signals from low-pass
filter (IC2551, pin 1) are applied to the AF switch (IC2601,
pins 1, 7).
The switched AF signals are amplified at the AF power
amplifier (IC2602, pins 1, 4) and then applied to the speaker
switch (Q2602).
The switched signal is applied to the internal speaker that is
connected to J2601 via [EXT SP] jack (J2602).
IC2551
IC2601
Q2602
IC2602
AF
IC2551
DSPO1
LOGIC UNIT
MAIN UNIT
3
1 5
7
7
1
6
6 6
6
[EXT SP]
AF amp.
SP1
CHASSIS
LPF
De-
emphasis
• AF CIRCUIT
LPF
LPF
IC451
LOGIC unit
MAIN UNIT
CODEC IC (IC551)
IC301
IC601
DSPO2
AF
signals
DSPI2
(16.15 kHz)
3rd IF
signal A/D
converter
D/A
converter
DSP IC
IC2201
DSP IC
• DSP CIRCUIT