Circuit Description; Frequency Configuration; Receiver; Receiver Section Configuration - Alinco DR-138 Service Manual

Frequency configuration

The receiver utilizes double conversion. The first IF is 38.850 MHz and the second IF is 450kHz. The
first local oscillator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the necessary frequencies. Fig. 1 shows the frequencies.
ANT
RF
ANT SW
AMP
POWER
AMP
AMP

Receiver

The receiver is double conversion super heterodyne, designed to operate in the frequency range of 136
to 173.9975MHz.
The frequency configuration is shown in Fig. 1.
 Front - end RF amplifier
An incoming signal from the antenna is applied to an RF amplifier (Q206) after passing through a
transmit/receive switch circuit (D210 are off) and a band pass filter (L206, L207 and varactor diodes :
D207, D208). After the signal is amplified (Q206), the signal is filtered through a band pass filter (L204,
L205 and varactor diodes: D205, D206) to eliminate unwanted signals before it is passed to the first mixer.
The voltage of these diodes are controlled by tracking the CPU (U2) center frequency of the band pass
filter. (See Fig. 2.)
ANT
Q206
BPF
RF AMP
ANT SW
D210,D211 D207, D208
TV
L206, L207
U505
CPU
D/A
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CIRCUIT DESCRIPTION

1st
MIX
RX
RF
TX
Fig. 1 Frequency configuration
MIXER
Q205
BPF
D205,D206
L204, L205
1st Local OSC
(PLL)
Fig. 2 Receiver section configuration
CF
450KHz
MCF
IF SYSTEM
38.850MHz
38.4M Hz
Q211
X2 M ULTIPLY
PLL
1/2
VCO
CF201(wide)
MCF
IF AMP
XF200, XF201
Q204
X200
TCXO
X 2 MULTIPLY
3
AF
AMP
TCXO
19.200MHz
MIC
AMP
CF200(Narrow) U505
D/A CONVERTER
U200
IF system
BUFFER AMP
U501(4/4)
Q211
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DR138
SP
MIC
W/NO