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3 - 3
3-1-5 1ST IF CIRCUIT
(RXPLL-A AND RXPLL-B UNITS)
The 1st IF circuit filters and amplifies the 1st IF signal. The
1st IF signal from the 1st mixer circuit is applied to an MCF
(Monolithic Crystal Filter) to suppress out-of-band signals.
• RX-A OR RX-ONLY CIRCUITS (RXPLL-A UNIT)
The filtered 1st IF signal from the low-pass filter passes
through the one of the three crystal bandpass (roofing) filters
(FI1401: bandwidth is 15 kHz, FI402: bandwidth is 6 kHz or
FI403: bandwidth is 3 kHz) via the FIL selectors (IC1402,
IC1403). The filtered signal is amplified at the 1st IF ampli-
fiers (Q1401–Q1403) via the low-pass filter (L1405, L1406,
C1420, C1421). The amplified 1st IF signal is applied to the
2nd mixer circuit.
• RX-B CIRCUIT (RXPLL-B UNIT)
The filtered 1st IF signals from the low-pass filter passes
through the one of the three crystal bandpass (roofing) filters
(FI1401: bandwidth is 15 kHz, FI1402: bandwidth is 6 kHz or
FI1403: bandwidth is 3 kHz) via the FIL selectors (IC1402,
IC1403). The filtered signal is amplified at the 1st IF ampli-
fiers (Q1401–Q1403) via the low-pass filter (L1405, L1406,
C1420, C1421), and is then applied to the 2nd mixer circuit.
3-1-6 2ND MIXER CIRCUIT
(RXPLL-A AND RXPLL-B UNITS)
The 2nd mixer circuit mixes the amplified 1st IF signal and
2nd LO signal for conversion into the 2nd IF signal.
• RX-A OR RX-ONLY CIRCUITS (RXPLL-A UNIT)
The 1st IF signal from the 1st IF amplifiers (Q1401–Q1403)
is applied to the 2nd mixer circuit (IC1501, pin 4, IC1502, pin
4) respectively. The applied signals are mixed with 2nd LO
signal from the RXPLL-A circuit to convert into 36 kHz 2nd
IF signal.
The 2nd IF signal from the 2nd mixer circuit (IC1501, pin 5)
is amplified at the buffer amplifier (Q1501), and is then
applied to the 2nd IF amplifier (IC1503, pin 3). The signal is
applied to the 90 degrees transphasor (IC1505, pin 6).
The 2nd IF signal from the other 2nd mixer circuit (IC1502,
pin 5) is amplified at the buffer amplifier (Q1502), and is then
applied to the 2nd IF amplifier (IC1504, pin 3). The signal is
applied to the 90 degrees transphasor (IC1505, pin 2).
The signals from the 90 degrees transphasor (IC1505, pins
1, 7) are applied to the compositor (IC1505, pins 9, 10). The
signal is amplified at other 2nd IF amplifier (IC1506), and is
then applied to the DSP-A board to demodulate 2nd IF sig-
nal.
A portion of 2nd IF signal from the compositor (IC1505, pin
8) is applied to the AGC detector circuit.
The 2nd mixer circuit has 2 mixers and 90 degrees
transphasor to improve image rejection ratio.
• RX-B CIRCUIT (RXPLL-B UNIT)
The 1st IF signal from the 1st IF amplifiers (Q1401–Q1403)
is applied to the 2nd mixer circuit (IC1501, pin 4, IC1502, pin
4) respectively. The applied signals are mixed with 2nd LO
signal from the RX-B circuit to convert into 36 kHz 2nd IF
signal.
The 2nd IF signal from the 2nd mixer circuit (IC1501, pin 5)
is amplified at the buffer amplifier (Q1501), and is then
applied to the 2nd IF amplifier (IC1503, pin 3). The signal is
applied to the 90 degrees transphasor (IC1505, pin 6).
The 2nd IF signal from the other 2nd mixer circuit (IC1502,
pin 5) is amplified at the buffer amplifier (Q1502), and is then
applied to the 2nd IF amplifier (IC1504, pin 3). The signal is
applied to the 90 degrees transphasor (IC1505, pin 2).
The signals from the 90 degrees transphasor (IC1505, pins
1, 7) are applied to the compositor (IC1505, pins 9, 10). The
signal is amplified at other 2nd IF amplifier (IC1506), and is
then applied to the DSP-B board to demodulate 2nd IF sig-
nal.
A portion of 2nd IF signal from the compositor (IC1505, pin
8) is applied to the AGC detector circuit.
The 2nd mixer circuit has 2 mixers and 90 degrees
transphasor to improve image rejection ratio.
IF_IN
6
7
1
IC331
switch
RXPLL-A/B
units
DSP-A/B units
36 kHz
3rd IF
signal
ADS signal
IC341,
IC371
IC301
IC501
IC771
IC701
to AF amplifier circuit
IC601,
IC651
Low-pass
filter
AGC
"AGC OUT" signal to
RXPLL-A/B units
"AGC DET" signal from
RXPLL-A/B units
Low-pass
filter
A/D
converter
(IC401)
5
DSP IC
(IC1)
D/A
D/A
converter
(IC551)
• DSP CIRCUIT (RECEIVER)
Summary of Contents for IC-7800
Page 1: ...SERVICE MANUAL ADDENDUM CONTENTS PARTS LIST 1 BOARD LAYOUTS 65 VOLTAGE DIAGRAM 67 Dec 2009 ...
Page 79: ...SERVICE MANUAL ADDENDUM CONTENTS PARTS LIST 1 BOARD LAYOUTS 60 VOLTAGE DIAGRAM 64 Feb 2009 ...
Page 157: ...SERVICE MANUAL ADDENDUM CONTENTS PARTS LIST 1 BOARD LAYOUTS 57 VOLTAGE DIAGRAM 59 Aug 2008 ...
Page 245: ...SERVICE MANUAL ADDENDUM CONTENTS PARTS LIST 1 BOARD LAYOUTS 57 VOLTAGE DIAGRAM 59 Jul 2008 ...
Page 333: ...THE TRANSCEIVER i7800 SERVICE MANUAL S 14015HZ C1 2 Mar 2006 ...
Page 555: ...1 1 32 Kamiminami Hirano ku Osaka 547 0003 Japan S 14015HZ C1 2 C 2004 2006 Icom Inc ...