Section 4 Circuit Descripiton; Receiver Circuits - Icom IC-R5 Service Manual

SECTION 4 CIRCUIT DESCRIPTION

4-1 RECEIVER CIRCUITS

4-1-1 BAND SWITCHING CIRCUIT (RF UNIT)
The RF signals from the antenna connector pass through the
limitter (D68) and an attenuator (D69). The signals are then
applied to the antenna switching circuit (D13, D31, D73, D75)
which suppress out-of-band signals.
4-1-2 RF CIRCUIT (RF UNIT)
The RF circuit amplifies the received signals within the range
of frequency coverage and filters out-of-band signals.
(1) 0.150 MHz–29.999 MHz
RF signals (0.150–29.999MHz) from an band switching cir-
cuit (D73) pass through a low-pass filter (C511–C515, L81,
L82). The filtered signals are amplified at an RF amplifier
(Q505) passing through each filters depending on the receiv-
ing frequency. The amplified signals are then applied to the
1st mixer circuit (IC1, pin 1) after being amplified at another
RF amplifier (IC11) via the band switching diode (D71).
The signals below 1.9 MHz pass through a low-pass filter
(C534, C535, C657, C658, L88, L89) via the band switching
diode (D66), and are then applied to the RF amplifier circuit
(Q505) via the band switching diode (D67).
The 1.9 MHz–14.995 MHz signals pass through the band
switching diode (D65) and bandpass filter (C522–C531,
L85–L87, L91), and are then applied to the RF amplifier cir-
cuit (Q505) via the band switching diode (D70).
• RF CIRCUIT
1st mixer
IC11
(IC1)
RF
2nd mixer
rcuit
1st LO
0.15 30 MHz
Q505
RF
BAND
SW
D36, D71
D25, D29,
BAND
D72
SW
D32, D34
BAND
SW
The 15 MHz–29.995 MHz signals pass through the band
switching diode (D63) and high-pass filter (C516–C520, L83,
L84) and are then applied to the RF amplifier circuit (Q505)
via the band switching diode (D64).
(2) 118 MHz–174.995 MHz, 330 MHz–832.995 MHz
RF signals (118 MHz–174.995 MHz, 330 MHz–832.995
MHz) from an antenna switching diode (D75) are passed
through each bandpass filter and RF amplifier, and are then
applied to the 1st mixer circuit (IC1) via the band switching
diode (D71) and RF amplifier (IC11).
The 118 MHz–174.995 MHz signals pass through the band
switching diode (D74) and low-pass filter (C8–C13, C67,
C416, L14, L57–L59, L70), and are then amplified at RF
amplifier (Q14). The amplified signal passes through the tun-
able band-pass filters (D1, D2) and band switching diode
(D25).
The 330 MHz–469.995 MHz signals are amplified at RF
amplifier (Q35) via the band switching diode (D3) and band-
pass filter (C19–C23, C216, L2–L5). The amplified signal
passes through the tunable band-pass filters (D4, D5) and
band switching diode (D29).
The 470 MHz–832.995 MHz signals are amplified at RF
amplifier (Q24) via the band-pass filter (C32, C33, C35–C37,
C39, C145), between the band switching diode (D11, D32).
Q501, D76
LPF
BAND BAND
BPF
SW
D63, D65,
D66
HPF
118 175 MHz
D1, D2
Q14
RF
BPF BPF
330— 470 MHz
D4, D5
Q35
RF
BPF BPF
470 833 MHz
Q24
RF
BPF
30 118 MHz, 175 330 MHz
Q36
RF
BPF
833 1309.995 MHz
Q26
RF
BPF
4 - 1
LIMITER
ANT
SW
BAND
LPF
SW
SW
D64, D67,
D70
D3, D11,
D74
BAND
SW
ANTENNA
ATT
D13, D31,
D73, D75