4 - 1
SECTION 4
CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS
4-1-1 DUPLEXER CIRCUIT (RF UNIT)
The transceiver has a duplexer (low-pass and high-pass fil-
ters) on the frist stage from the antenna connector to sepa-
rate the signals into below UHF and SHF signals. The high-
pass filter (L51–L55, C41–C46 and C48–C50) is for SHF
(1200 MHz) signal and the low-pass filter (C9, C10,
C12–C14 and L7–L9) is for below UHF (50 MHz, 144 MHz,
440 MHz and WFM) signals. The filtered SHF signal is
applied to the low-pass fileter (C51–C54, L56 and L57).
The RF signals below UHF pass through the duplexer circuit
and are separated into VHF (50 MHz, 144 MHz and WFM
band) and UHF (440 MHz band) signals. The high-pass fil-
ter (C4–C8, L5, L6) is for UHF (440 MHz band) signal and
the low-pass filter (C15–C20, L10–L12) is for VHF (50 MHz,
144 MHz and WFM band) signals.
The VHF signals are applied to the another duplexer circuit
for separation into 50 MHz and above WFM band signals.
The high-pass filter (C21–C24, C84 and L13–L15) is for 144
MHz and WFM band signals and the low-pass filter
(C27–C33 and L16–L18) is for 50 MHz band signal.
The separated signals are applied to each RF circuits.
4-1-2 ANTENNA SWITCHING CIRCUITS (RF UNIT)
The antenna switching circuit functions as a low-pass filter
while receiving. However, its impeadance becomes very
high while transmitting by applying a current to D101 and
D102 (50 MHz), D302 and D303 (144MHz and WFM), D402
and D403 (440 MHz), D51 and D52 (1200 MHz).
Thus, transmit signals are blocked from entering the receiv-
er circuits. The antenna switching circuit employs a 1/4
λ
type diode switching system. The passed signals are then
applied to each RF amplifier circuit.
4-1-3 50 MHz BAND RF CIRCUIT (RF UNIT)
The RF circuit amplifies signals within the range of frequen-
cy coverage and filters out-of-band signals.
The signals from the antenna switching circuit (D101 and
D102) are amplified at the RF amplifier (Q101). The ampli-
fied signals pass through the tunable bandpass filter
(L108–L110, C115, C117, C120, D106, D107) to suppress
out-of-band signals, and are then applied to the 1st mixer
circuit (IC601, pin 1).
4-1-4 144 MHz AND WFM BANDS RF CIRCUITS
(RF UNIT)
The signal from the antenna switching circuit (D302, D303)
are applied to the each band-pass fileters and RF amplifier.
• RF signals 144 MHz band
The 144 MHz band signals are applied to the RF amplifier
(Q301) via the tunable bandpass filter (L303, L304, C306,
D306). The amplified signals pass through the tunable band-
pass filter (C318–C321, D309, D310, L305, L306), and are
then applied to the 1st mixer circuit (IC601, pin 1).
• RF CIRCUIT
1st mixer
HPF
LPF
ANT
SW
RF
BPF
RF
BPF
ANT
SHF band
(1200 MHz)
LPF
ANT
SW
RF
BPF
RF
UHF band
(440 MHz)
HPF
HPF
ANT
SW
BPF
RF
BPF
VHF band
(144 MHz)
LPF
BPF
RF
BPF
WFM band
(RX only)
ANT
SW
RF
BPF
VHF band
(50 MHz)
LPF
IC601
1st LO
BPF
XTAL
BPF
CERAMIC
D601
Mode
SW
D602
Mode
SW
FM mode
FI601
69.45 NHz
WFM mode
FI602
13.35 NHz
LEVEL
CONV.
D51, D52
Q51
FI51
IC51
FI52
D402, D403
Q401
FI401
IC501
D302, D303
D306
Q301
D309, D310
D202
Q201
D203
Q101
D106,
D107
D101,
D102
to IF amp.
(Q701)
Q9
"TUNE" signal from IC5, pin 11 (LOGIC unit)
