Icom IC-R20, Руководство по обслуживанию

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4 - 1
4-1 RECEIVER CIRCUITS
4-1-1 BAND SWITCHING CIRCUIT (RF UNIT)
The RF signals from the antenna connector pass through
the limiter (D68) and an attenuator* (D69). The signals are
then applied to the antenna switching circuit (D3, D11, D13,
D65, D66 and D73–D75 ).
*Above 2 GHz RF signals do not pass through the attenua-
tor.
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.
• A-BAND CIRCUIT
(1) MF (above 0.15 MHz, below 1.9 MHz) signals
RF signals (0.15–1.9 MHz) from an attenuator (D69) pass
through the low-pass filter (L123–L125 and C851–C853),
band switch (D66) and another low-pass filter (L88, L89,
C533–C535, C657, C658). The filtered signals pass through
another band switch (D67), and are then amplified at an RF
amplifier (Q505). The amplified signals are applied to the
next band switch (D72).
(2) HF-L (above 1.9 MHz, below 15 MHz) signals
RF signals (1.9–15 MHz) from an attenuator (D69) pass
through the low-pass filter (L123–L125 and C851–C853),
band switch (D65) and bandpass filter (L85–L87, L91,
C522–C531 and C891). The filtered signals pass through
another band switch (D70), and are then amplified at an RF
amplifier (Q505). The amplified signals are applied to the
next band switch (D72).
SECTION 4 CIRCUIT DESCRIPTION
RF
RF
BPF
BPF
BPF
RF
BPF
BPF
Pre
Amp
Pre
Amp
HF-L (1.9 15 MHz)
MF (15 30 MHz)
A-VHF (118 175 MHz)
B-VHF (118 175 MHz)
30 300M (30 300 MHz except A-VHF range)
A-UHF (300 470 MHz)
800M (470 833 MHz)
1G (833 1305 MHz)
B-UHF (300 470 MHz)
MF (0.15 1.9 MHz)
from the
bar antenna
HPF
HPF
LPF
LPF
LPF
LIMITER
BAND
SW
BAND
SW
BAND
SW
BAND
SW
BAND
SW
BAND
SW
BAND
SW
ANTENNA
ATT
ANT
SW
to 2nd mixer
circuit
RF-A circuit
RF-B circuit
1st mixer
1st mixer
to 2nd mixer
circuit
LO (1001 or 2002MHz)
RF
IC2 IC3
mixer
1305 3305 MHz
RF
RF
BPF
RF
BPF
RF
BPF
RF
RF
RF
BPF
BPF
HPF
Q505
Q36
Q550
Q14
Q549
Q551
Q35
Q548
Q24
Q25
IC18
IC15
IC1
IC19
• RF CIRCUITS