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SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVE CIRCUITS
4-1-1RF CIRCUITS (MAIN UNIT)
This transceiver has 4 RF circuits to provide wide receiving
range. The received signals from the antenna connector
(CHASSIS; J1) are applied to each RF circuits for the frequency
coverage, and amplified within the frequency coverage.
• While receiving 0.495–76 MHz
The 0.495–76 MHz band signals are passed through the
three low-pass filters (LPF; L32, L34, L39, L42, C284, C290,
C294, C307, C314), then applied to the RF amplifier (Q38)
via the band switches (D30, D43) and LPF or BPF.
The 0.495–30 MHz band signals are passed through the
LPF (L20, C241, C242, C247), the 30–76 MHz signals are
passed through the Bandpass Filter (BPF; D39, L21, L24,
C238, C256) before being applied to the RF amplifier (Q38).
The amplified signals are applied to the 1st mixer (IC16, pin
1) via the band switch (D16).
- 0.495–76 MHz -
• While receiving 76–300 MHz
The 76–300 MHz band signals are passed through two LPFs
(L39, L42, C307, C314) and a couple of High-pass Filter (HPF;
L33, C287, C293) and LPF (L29, L31, C266, C269, C276,
C283, C514, C516), then applied to the RF amplifier (Q42) via
the antenna switching circuit (D35, D38) and the LPF (D53,
L44, C295, C303).
The amplified signals are then applied to the 1st mixer (IC16, pin
1) via the BPF (D27, D28, D31, D36, L10, L11, L22, L23, C208,
C210, C216, C228, C233, C243) and band switch (D21).
- 76–300 MHz -
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to the
1st mixer
(IC16, pin 1)
0.495–30 MHz
D39
D16
D30
Q38
D43
D44
30–76 MHz
from the
antenna
RF
amp
LPF
ATT
BPF
LPF
LPF
3 LPF’s
to the
1st mixer
(IC16, pin 1)
D21
D53
D27, D28,
D31, D36
Q42
from the
antenna
BPF
LPF
LPF
LPF
HPF
LPF
RF
amp
2 LPF’s
D35, D38
ANT
SW
• While receiving 300–500 MHz
The 300–500 MHz band signals are passed through the LPF
(L42, C314) and a couple of HPF (L38, C302, C306) and
LPF (D41, D45, L26, L30, C255, C257, C262, C275, C282,
C289, C515), then applied to the RF amplifier (Q43) via the
antenna switching circuit (D34, D37) and the BPF (D55, L36,
L106, C304, C522, C523).
The amplified signals are then applied to the 1st mixer
(IC16, pin 1) via the BPF (D26, D32, L13, L25, C204, C215,
C222, C236, C244, C520, C521) and band switch (D22).
- 300–500 MHz -
to the
1st mixer
(IC16, pin 1)
D55
D41, D45D26, D32
D22
Q43
LPF
BPFBPF
HPF
LPF
from the
antenna
RF
amp
D34, D37
ANT
SW
• While receiving 500–999 MHz
The 500–999 MHz band signals are passed through the HPF
(L41, C311, C313) and band switch (D54), then applied to
the RF amplifier (Q45) via the attenuator (D46). The amplified
RF signals are applied to another RF amplifier (Q39) via the
BPF (D33, D40, L15, L27, L28, C229, C237, C245, C252,
C261). The amplified RF signals are then applied to the 1st
mixer (IC16, pin 1) via the band switch (D23).
- 500–999 MHz -
to the
1st mixer
(IC16, pin 1)
D23
Q39 Q45
D54
D46
ATT
from the
antenna
HPF
BPF
RF
amp
RF
amp
D33, D40
4-1-2 1ST IF CIRCUITS (MAIN UNIT)
The 1st IF circuits contain the 1st mixer, 1st IF amplifier
and the 1st IF fi lter. The 1st IF mixer converts the received
signals into a fixed frequency of the 1st Intermediate
Frequency (IF) signal. The converted 1st IF signal is fi ltered
at the 1st IF fi lters, then amplifi ed at the 1st IF amplifi er.
The received signals from the RF circuits are applied to the
1st IF mixer (IC16, pin 1), and converted into the 46.35 MHz
(AM/FM)/14.85 MHz (WFM) 1st IF signal by being mixed
with 1st Local Oscillator (LO) signals from the VCOs (VCO
BOARD).
While receiving 0.5–76 MHz band signals, the 1st LO signals
are generated at 50 MHz VCO (VCO BOARD; Q10, Q13,
D7, D8), and for receiving 76–280 MHz band signals, the 1st
LO signals are generated at 144 MHz VCO (VCO BOARD;
Q9, Q12, D6).
While receiving 280–999 MHz band signals, the 1st LO
signals are generated at 430 MHz VCO (VCO BOARD; Q8,
Q11, D5). If the receiving frequency is 500 MHz and above,
the VCO output signal is doubled at the doubler circuit (Q18)
before being to applied to the 1st mixer (IC16, pin 3).
The converted IF signal is passed through the 1st IF filter
FI3 (AM/FM mode) or FI2 (WFM mode) to filter out the
unwanted signal, then applied to the 1st IF amplifier (Q9).
The amplifi ed 1st IF signal is then applied to the FM IF IC
(IC15, pin 16).
• 1st IF CIRCUIT