Icom IC-R3 Service Manual page 8

The 65 MHz–107.995 MHz signals pass through the band
switching diode (D503) and bandpass filter (D501), and are
then amplified at the RF amplifier (Q501). The amplified sig-
nals pass through the bandpass filter (D502) and band
switching diode (D504).
The 108 MHz–173.995 MHz signals pass through the band
switching diode (D603) and bandpass filter (D601), and are
then amplified at the RF amplifier (Q601). The amplified sig-
nals pass through the bandpass filter (D602) and band
switching diode (D604).
The 174 MHz–224.995 MHz signals pass through the band
switching diode (D703) and bandpass filter (D701), and are
then amplified at the RF amplifier (Q701). The amplified sig-
nal pass through the bandpass filter (D702) and band
switching diode (D704).
(3) 330 MHz–469.995 MHz
RF signals (330 MHz–469.995 MHz) from the RF switching
circuit pass through the band switching diode (D21) and a
bandpass filter (C19–C27, L2–L5, L39). The filtered signals
are amplified at an RF amplifier (Q7), and then passed
through the bandpass filter (D22, D23). The filtered signals
are then applied to the 1st mixer circuit (IC1) via the band
switching diode (D24).
(4) 470 MHz–799.995 MHz
RF signals (470 MHz–799.995 MHz) from the RF switching
circuit pass through the band switching diode (D805) and a
low-pass filter (C321–C325, L81, L82). The filtered signals
are passed through each bandpass filter and RF amplifier
depending on the receiving frequency. The amplified signals
are then applied to the 1st mixer circuit (IC1) via the band
switching diode (D804 or D854) respectively.
The 470 MHz–599.995 MHz signals pass through the band
switching diode (D803) and bandpass filter (D801), and are
then amplified at the RF amplifier (Q801). The amplified sig-
nals pass through the bandpass filter (D802) and band
switching diode (D804).
The 600 MHz–799.995 MHz signals pass through the band
switching diode (D853) and bandpass filter (D851), and are
then amplified at the RF amplifier (Q851). The amplified sig-
nals pass through the bandpass filter (D852) and band
switching diode (D854).
1ST MIXER CIRCUIT (RF UNIT)
"RFO" signals from
the each front-end circuit C153
1
2
1st mixer IC (IC1)
3
C152
R256
R255
R257
(5) 225 MHz–329.995 MHz AND 800 MHz–1149.995 MHz
RF signals (225 MHz–329.995 MHz and 800 MHz–1149.995
MHz) from the RF switching circuit pass through the band
switching diode (D33). The signals are passed through each
bandpass filter and RF amplifier depending on the receiving
frequency. The amplified signals are then applied to the 1st
mixer circuit (IC1) via the band switching diodes (D35 or
D36) respectively.
The 225 MHz–329.995 MHz signals pass through the band-
pass filter (C40–C43, C395, C396, L58, L59), and are then
amplified at the RF amplifier (Q9). The amplified signals
pass through the band switching diode (D35).
The 800 MHz–1149.995 MHz signals pass through the
bandpass filter (C46–C49, C51–C54, L11–L14), and are
then amplified at the RF amplifier (Q8). The amplified sig-
nals pass through the band switching diode (D36).
4-1-3 1ST MIXER CIRCUIT (RF UNIT)
The 1st mixer circuit converts the received RF signals to a
fixed frequency of the 1st IF signal with a PLL output fre-
quency. By changing the PLL frequency, only the desired
frequency will pass through the bandpass filters at the next
stage of the 1st mixer.
The filtered or amplified RF signals from each RF circuit are
mixed with 1st LO signal at the 1st mixer circuit (IC1) to pro-
duce each 1st IF signal depending on the receiving fre-
quency. The 1st IF signal is output from pin 6, and passed
through the bandpass filter (FI904) to suppress unwanted
harmonic components. The filtered 1st IF signal is applied to
the 2nd mixer circuit.
FM, AM, WFM
1ST IF
240.1 MHz
1
*
30–799.995 MHz and 1321–2099.995 MHz range
* 2
800–1320.995 MHz and 2100–2450.095 MHz range
The 1st LO signals are generated at the 1st VCO (VCO unit;
Q22, Q23, D62) and are applied to the 1st mixer (IC1, pin 3)
directly or passed through the doubler circuit (Q26) after
being amplified at the buffer amplifier (VCO unit; IC4).
C234
6
5
4
C70
"1st VCO" signal from
the 1st VCO circuit (VCO unit)
4 - 2
C3F (TV)
241.85* 1 , 238.35*
"1st IF" signal to
the 2nd mixer circuit
"1st IF" signal to
the FM-TV unit
"R3V" signal from
the LOGIC unit
2 MHz