RTS DV 2400 Series, Service Manual, Page: 2 / 40

DV-2400
1
CIRCUIT DESCRIPTION
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 SW
MCF
38.8 50MHz
IF SYSTEM
45 0KHz
CF
ANT
AF
AMP
SP
TCXO 19 .200MHz
POWER
AMP
RF
AMP
PL L
VCO
MIC
MIC
AMP
RX
TX
1s t
MIX
RF
AMP
1/2
MUL TIPLY
38.4MHz
X2
Fig. 1 Frequency configuration
Receiver
The receiver is double conversion super heterodyne, designed to operate in the frequency range of 400
to 490MHz.
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 (D213 are off) and a band pass filter (L207, L208, L211 and varactor diodes:
D207, D208). After the signal is amplified (Q206), the signal is filtered through a band pass filter (L205,
L206 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 D/A (U505) center frequency of the band
pass filter. (See Fig. 2.)
ANT SW
IF system
(PLL)
CF201(wide)
ANT
1st Local OSC
BUFFER AMP
U501(4/4)
U200
IF AMP
Q204
MCF
XF200, XF201
MIXER
Q205
BPF
RF AMP
Q206
BPF
U505
D/A
TV
CPU
CF200(Narrow)
D/
D207, D208
L207, L208, L211
D205,D206
L205, L206
A CONVERTER
U505
W/NO
X2 MULTIPLY
Q200
TCXO
X200
Fig. 2 Receiver section configuration