Icom IC-R100 Service Manual page 8

4-2 IF CIRCUITS
4-2-1 TUNER UNIT (PLL UNIT)
The TUNER UNIT (EP2) contains an RF amplifier controlled
by the ТАСС signal, mixer and 4 VCOs.
Тһе RF signals
are applied to P2 on the TUNER UNIT (EP2) to be con-
verted to а 46 MHz IF signal. Тһе TUNER UNIT (EP2)
outputs the signal from pin 8. IC2 on the LOGIC UNIT
supplies 2-bit data to IC11 (pin 3, 4). IC11 is ап expander
for switching the operating band of TUNER UNIT (EP2).
The following table (Fig 2) shows the relations between
2-bit data and the band signal.
H: High level No indication: Lovv level
4-2-2 AMIFM IF AND 2ND MIXER CIRCUITS
(MAIN UNIT)
The 46 MHz IF signal passes through a switching diode
(D1) with AM 5 and FM 5 signals when AM or FM mode
is selected. The signal is applied to an IF amplifier
and then applied to a crystal filter (ЕП) to improve the
selectivity.
The filtered signal is applied to a 2nd mixer (Q2) and
then mixed with the 35.3 MHz 2nd LO signal to produce
a 10.7 MHz 2nd IF signal.
A 35.3 MHz 2nd LO signal is generated by a 2nd local
oscillator circuit consisting of D8, X3, Q5, and other
components. The 2nd LO oscillator circuit produces a
frequency step less than the PLL reference frequency.
The LOGIC UNIT supplies D/A converted signals to IC10
(pin 3) which correspond to each tuning step. The
signals are amplified at IC10 and then applied to a
varactor diode (D8) which shifts the oscillation frequency.
• АМІЕМ IF AND 2ND MIXER CIRCUITS
46.0 MHz 10.7 MHz
Q1
IF |
PLL IC
signal (IC1,
pin 16)
AM, FM 35.3 MHz
signal
DIA signal
from
LOGIC UNIT
Fig. 3
4—2
4-2-3 2ND IF AND FM DEMODULATOR
CIRCUITS (MAIN UNIT)
The 2nd IF signal is applied to a 3rd mixer section of
IC1 and is mixed vvith a 3rd LO signal to be converted
to a 455 kHz 3rd IF signal.
IC1 is designed for use in FM dual conversion com-
munications equipment. IC1 contains the 3rd mixer,
local oscillator circuit, limiter amplifier, quadrature
detector circuit, and active filter circuit. The local
oscillator section and X1 generate 10.245 MHz for a
3rd LO signal.
The 3rd IF signal from the 3rd mixer (IC1, pin 3) passes
through a ceramic filter (F13) where unwanted signals are
suppressed. It is then amplified at the limiter amplifier
section (IC1, pin 5) and applied to the quadrature detector
section (IC1, pin 8 and ceramic discriminator X2) to
demodulate the 3rd IF signal into an AF signal. The AF
signal is output from IC1 (pin 9).
4-2-4 AM DEMODULATOR CIRCUIT
(MAIN UNIT)
A portion of the 455 kHz 3rd IF signal is applied to an IF
amplifier (Q4) after passing through the ceramic filter (FI3)
when AM mode is selected by switching diodes (D5, D7).
When the switching diodes are turned ON, AM 5 signal
line obtains 5 V. The amplified signal passes through
a ceramic filter (Fl4) to improve selectivity. The filtered
signal is re-amplified at an IF amplifier (Q7) and then
rectified by the AM detector circuit (D10, D11). The
detected signal is demodulated into an AM signal.