RTS DV-3066, Руководство по обслуживанию, Страница: 2 / 30

DV3066
1
CIRCUIT DESCRIPTION
1. Frequency Configuration
The frequency configuration is shown in Figure 1 and
Table 1.
ANT SW
RF
AMP
MCF
38.850MHz
IF SYSTEM
450KHz
CF
ANT
AF
AMP
SP
PLL
VCO
MIC
MIC
AMP
MIX
TCXO
19.200MHz
MULTIPLY
38.40MHz
RX/TX:66 ~ 88MHz
FINAL
PRE
DRIVE
DRIVE
Fig. 1 Frequency configuration
Reception method
Double super heterodyne
1st IF Frequency 38.85MHz (Upper)
2nd IF Frequency 450kHz (Lower)
Transmission method VCO direct oscillation amplification
Modulation Variable reactance phase modulation
Table 1 Basic configuration
2. Receiver
2-1. Front-end RF Amplifier
The received signal from the antenna passes through a
low pass filter and then through a transmit/receive switching
circuit (antenna switch) and enters the band-pass filter
(L520, L521).
The signal passing through the band-pass filter (L520,
L521) is amplified by with an RF amplifier (Q506), passes
through a band-pass filter (L524, L522) and enters the first
mixer (Q507).
These band-pass filters are tuned to a desired frequency
by varicaps (D507, D508, D509, D510). A tuning voltage
corresponding to the desired signal is applied to each
varicap through the P76 terminal (pin 32) of the MPU (U201)
to tune to the receive frequency. (See Fig. 2)
2-2. First Mixer
The received signal passing through the band-pass filter
(L524, L522) is mixed with the first local signal generated by
the VCO by the first mixer (Q507) to produce a first IF signal
(38.85 MHz) (Upper heterodyne). The first IF signal passes
through a MCF (Monolithic crystal filter: XF3000 and
XF3001) to remove unwanted components.
The first IF signal passing through the MCF (XF3000 and
XF3001) is amplified by an IF amplifier (Q511) and the
resulting signal enters the FM IC (U503).
ANT SW
IF,MIX,DET
LV
CF500
ANT
1st Local OSC
U503
IF AMP
Q511
MCF
XF3000,XF3001
MIXER
Q507
BPF
RF AMP
Q506
BPF
D506
2nd Local OSC
D501,D502
.
Q512
X2
TCXO
19.200MHz
X500
VCO PLL
(PLL)
CF3000
MULTIPLY
AF AMP
SP
AF PA AMP
U205
VFO
U201
MPU
U204A
Tuning voltage
Fig.2
2-3. IF Amplifier Circuit
The first IF signal (38.85 MHz) amplified by the IF
amplifier (Q511) and the second IF signal (38.40 MHz)
generated by tripling the 19.200 MHz reference oscillator
frequency of the TCXO (X500) by Q512, are mixed in the
FM IC to produce a second IF signal (450 kHz) (Lower
heterodyne). The second IF signal passes through a
ceramic filter (CF3000) to remove unwanted components.
The second IF signal passing through the ceramic filter
(CF3000) passes through the IF amplifier in the FM IC
again and is detected to produced an audio signal. (See
Fig.2)
2-4. Wide/Narrow Switching Circuit
Narrow and Wide settings can be made for each channel
by switching the demodulation level. The WIDE (high level)
and NARROW (low level) data is output from U201, pin 11.
When a WIDE (high level) data is received, Q503 and
Q509 turn on.
When a NARROW (low level) data is received, Q503 and
Q509 turn off.
Q503 and Q509 turns on/off with the Wide/Narrow data and
the U503 detector output level is switched to maintain a
constant output level during wide or narrow signals. (See
Fig.3)
QUAD
AFOUT
C654
T3000
R596
R509
Q509
Q511
U503
FM SYSTEM
IFOUT
5R
P63 (U201)
H:Wide
L:Narrow
Q503
Fig.3