1-4 (No.RA003<Rev.004>)
SECTION 1
PRECAUTION
This service manual does not describe PRECAUTION.
SECTION 2
SPECIFIC SERVICE INSTRUCTIONS
2.1
CIRCUIT DESCRIPTION
2.1.1 Frequency Configuration
The receiver utilizes double conversion. The first IF is 49.95MHz and the second IF is 450kHz. The first Local oscillator is supplied
from the PLL circuit.
The PLL circuit in the transmitter generates the necessary frequencies. Figure 1 shows the frequencies.
Fig.1 Frequency configuration
2.1.2 Receiver System
The receiver system is shown in Figure 2.
Fig.2 Receiver system
2.1.2.1
Front End (RF Amplifier) Circuit
The signal coming from the antenna passes through the transmit/receive switching diode circuit (D201, D202, D203 and D204) and a
BPF (L415 and L416), and is then amplified by the RF amplifier (Q405).
The resulting signal passes through a BPF (L410,L411 and L413) and goes to the mixer. The BPF is adjusted by variable capacitance
diodes (D400, D401, D402, D403 and D404). The input voltage to the variable capacitance diodes is the regulated voltage output from
the DC amplifier (IC704).
2.1.2.2
First Mixer
The signal from the front end is mixed with the first local oscillator signal generated in the PLL circuit by Q404 to produce the first IF
frequency of 49.95MHz.
The resulting signal passes through the XF400 MCF to cut the adjacent spurious and provide optimum characteristics, such as adja-
cent frequency selectivity.
TX/RX: 450~520MHz (K, M)
TX/RX: 400~470MHz (K2, P, M2, M3)
TX/RX: 350~400MHz (K3)
400.05~
470.05MHz (K, M)
350.05~
420.05MHz (K2, P, M2, M3)
300.05~350.05MHz (K3)
450~520MHz (K, M)
400~470MHz (K2, P, M2, M3)
350~400MHz (K3)
1st MIX
MCF
SP
MIC
ANT
ANT
SW
RF
AMP
IF
System
x3
Tripler
PLL
VCO
49.95MHz
50.4MHz
TX
AMP
RF
AMP
AF
AMP
MIC
AMP
Baseband
TCXO
16.8MHz
SP
ANT
IC400
IF,MIX,DET
Q404
1st MIX
ANT
SW
Q400
x3 Tripler
2nd Local
X1
TCXO
16.8MHz
Baseband
IC705
BPF1
BPF
Q405
RF AMP
XF400
MCF
Q403
IF AMP
IC709
AF PA
(INT)
BPF1
1st Local
BPF
