Icom IC-80AD Service Manual page 10

1ST IF CIRCUIT (MAIN UNIT)
The RX signals from the RF circuits are applied to the 1st
mixer (RF: IC900) to be converted into the 1st IF signal,
by being mixed with the 1st Local Oscillator (LO) signals
from the VCO UNIT. The 1st LO signals from the VCO UNIT
are applied to the 1st mixer via the LO SW, or doubler (in
receiving of 600 MHz and above).
The converted 1st IF signal is passed through the IF SW (D2)
which toggles the path of the 1st IF signal: WFM mode or
other than WFM mode.
• FM/AM/DV MODE
The 1st IF signal from the 1st mixer (RF: IC900) is entered
to the MAIN UNIT, and passed through the 1st IF filter (FI50)
via IF SWs (D2, 3) to remove unwanted signals. The filtered
1st IF signals are applied to the 1st IF AMP (Q100), and the
amplified 1st signal is applied to the 2nd IF circuit.
• WFM MODE (Incl. 2nd IF circuit)
When receiving in WFM mode, the 1st IF signal from the 1st
mixer (RF: IC900) is entered to the MAIN UNIT and passed
through the IF SW (D2) and BPF, then applied to the 1st IF
AMP (Q1). The amplified 1st IF signal is applied to the 2nd
mixer (Q2) to converted into the 13.35 MHz 2nd IF signal,
by being mixed with the 45.9 MHz 2nd LO signal (generated
by X450, tripled by Q451). The converted 2nd IF signal is
passed through the 2nd IF filter (FI2) to remove sideband
noise, then applied to the 2nd IF AMP (Q100) via the IF SW
(D3). The amplified 2nd IF signal is applied to the 3rd IF
circuit.
• 1ST IF CIRCUIT
MAIN UNIT VCO UNIT
BC BAND; Q1,2,D1-3,5,6
VHF BAND; Q51,52,D51-55
UHF BAND; Q101,102,D100-104
FI50
D3
To the IF IC
XTAL
(IC100) IF BPF
M ODE
AM P SW
FM/AM/DV:61.65 MHz
Q100
FI2
CERAMIC
WFM:13.35 MHz
Q451
X450
X3
15.3MHz
Reference frequency
oscillator
D100
D850
TX circuits
LO
VCOs
SW
X2
Q850
D2
From the RF
IC900
circuits
M ODE
SW
1st IF mixer
BPF
Q2
IF
BPF
AM P
2ND IF AND DEMODULATOR CIRCUITS (MAIN UNIT)
<For FM, AM and DV mode>
The 1st IF signal from the 1st IF AMP (Q100) is applied to
the IF IC (IC100). The applied 1st IF signal is mixed with
the 61.2 MHz 2nd LO signal (generated by X450, buffered
by Q452) at the internal 2nd mixer, to be converted into the
450 kHz 2nd IF signal. The converted 2nd IF signal is output
from pin 3.
• FM MODE
The 2nd IF signal from the IF IC is passed through the 2nd
IF filter (FI100) via IF SWs (D102, 103). The filtered 2nd
IF signal is backed to the IF IC from pin 5, and saturation-
amplified by the internal limit AMP. The amplified 2nd IF
signal is FM-demodulated by the discriminator (X100), and
the recovered AF signals (RX AF signals) are output from
pin 9, then applied to the AF circuits via the FM mode SW
(IC500D, pins 8, 9).
• AM MODE
The 2nd IF signal from the IF IC is passed through the 2nd
IF filter (FI200) via IF SWs (D150, 151). The filtered 2nd IF
signal is amplified by 2nd IF AMP (Q103), then applied to
the AM demodulator circuit (Q104) to be recovered to the
AF signals. The demodulated AF signals are applied to the
AF circuits via the AM mode SW (IC500A).
• DV MODE
The 2nd IF signal from the IF IC is passed through the 2nd
IF filter (FI100) via IF SWs (D102, 103). The filtered 2nd
IF signal is backed to the IF IC from pin 5, then saturation-
amplified by the internal limit AMP. The amplified 2nd IF
signal is FM-demodulated by the discriminator (X200), and
the recovered AF signals (RX AF signals) are output from
pin 9, then applied to the AF circuits via the AF mute SW
(IC500, pins 4, 3).
• 3RD IF CIRCUIT (MAIN UNIT)
<For WFM mode only>
The 2nd IF signal from the 2nd IF AMP (Q100) is applied to
the IF IC.
The applied 2nd IF signal is mixed with the 15.3 MHz 3rd
LO signal (generated by X450, buffered by Q452), to be
converted into the 1.95 MHz 3rd IF signal by the internal 3rd
mixer. The converted 3rd IF signal is output from pin 3, and
passed through the IF SWs (D105, 106), then backed to the
IF IC (bypassing FI100). The 3rd IF signal is FM-demodulated
by the discriminator (X100), and the recovered AF signals
(RX AF signals) are output from pin 9, then applied to the AF
circuits via the WFM mode SW (IC500C, pins 8, 9).
• 2ND IF AND DEMODULATOR CIRCUITS
MAIN UNIT
Q104
Q103
AM IF
DET AM P
IC500A
AM
MODE
SW
IC500D
FM
MODE
To the AF filter
SW
(IC501)
IC500C
WFM
MODE
To the mode Sw
SW
(IC501)
To the buffer
(IC504B)
4 - 2
D151 FI200 D 150
CERAMIC
MODE M ODE
SW BPF SW
FI100
CERAMIC
BPF
D103
D102
D106
D105
MODE MODE
SW SW
IC100
From the IF AMP (Q100)
FM
DET
X100
DISCRI
D450 Q452
WFM15.3MHz
X1
M ODE
or
SW FM61.2MHz
X4
X450
15.3MHz