Kenwood 762G Manual Do Utilizador
24
TK-760G/762G
Frequency Configuration
The receiver utilizes double conversion. The first IF is
49.95MHz and the second IF is 450kHz. The first local oscil-
lator signal is supplied from the PLL circuit.
lator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the neces-
sary frequencies. Figure 1 shows the frequencies.
Fig. 1
Frequency configuration
Receiver System
The receiver is double conversion superheterodyne. The
frequency configuration is shown in Figure 1.
■ Front-end RF Amplifier
An incoming signal from the antenna is applied to an RF
amplifier (Q27) after passing through a transmit/receive
switch circuit (D33 and D34 are off) and a band pass filter
(L18). After the signal is amplified (Q27), the signal is fil-
tered through a band pass filter (L11, L13 and L15) to elimi-
nate unwanted signals before it is passed to the first mixer.
Band pass filters (L18, L11, L13 and L15) have varactor di-
odes (D30, D31, D18, D23 and D28).
switch circuit (D33 and D34 are off) and a band pass filter
(L18). After the signal is amplified (Q27), the signal is fil-
tered through a band pass filter (L11, L13 and L15) to elimi-
nate unwanted signals before it is passed to the first mixer.
Band pass filters (L18, L11, L13 and L15) have varactor di-
odes (D30, D31, D18, D23 and D28).
The voltage of these diodes are controlled by to track the
CPU (IC502) center frequency of the band pass filter. (See
Fig. 2)
Fig. 2)
■ First Mixer
The signal from the RF amplifier is heterodyned with the
first local oscillator signal from the PLL frequency synthe-
sizer circuit at the first mixer (Q15) to create a 49.95MHz
first intermediate frequency (1st IF) signal. The first IF signal
is then fed through two monolithic crystal filters (MCFs :
XF1) to further remove spurious signals.
sizer circuit at the first mixer (Q15) to create a 49.95MHz
first intermediate frequency (1st IF) signal. The first IF signal
is then fed through two monolithic crystal filters (MCFs :
XF1) to further remove spurious signals.
■ IF Amplifier
The first IF signal is amplified by Q13, and the enters IC5
(FM processing IC). The signal is heterodyned again with a
second local oscillator signal within IC5 to create a 450kHz
second IF signal. The second IF signal is then fed through a
450kHz ceramic filter (Narrow : CF1, Wide : CF2) to further
eliminate unwanted signals before it si amplified and FM
detected in IC5.
second local oscillator signal within IC5 to create a 450kHz
second IF signal. The second IF signal is then fed through a
450kHz ceramic filter (Narrow : CF1, Wide : CF2) to further
eliminate unwanted signals before it si amplified and FM
detected in IC5.
Item
Rating
Nominal center frequency
49.95MHz
Pass bandwidth
±
5.0kHz or more at 3dB
35dB stop bandwidth
±
20.0kHz or less
Ripple
1.0dB or less
Insertion loss
5.0dB or less
Guaranteed attenuation
80dB or more at fo
±
1MHz
Spurious : 40dB or more within fo
±
1MHz
Terminal impedance
350
Ω±
5% / 5.5pF
±
0.5pF
Table 1
Crystal filter (L71-0551-15) : XF1
Item
Rating
Nominal center frequency
450kHz
6dB bandwidth
±
4.5kHz or more
50dB bandwidth
±
10.0kHz or less
Ripple
2.0dB or less
Insertion loss
6.0dB or less
Guaranteed attenuation
55.0dB or more within fo
±
100kHz
Terminal impedance
2.0k
Ω
Table 2
Ceramic filter (L71-0959-05) : CF1
Item
Rating
Nominal center frequency
450kHz
6dB bandwidth
±
6.0kHz or more
50dB bandwidth
±
12.5kHz or less
Ripple
3.0dB or less
Insertion loss
6.0dB or less
Guaranteed attenuation
35.0dB or more within fo
±
100kHz
Terminal impedance
2.0k
Ω
Table 3
Ceramic filter (L72-0973-05) : CF2
Fig. 2
Receiver system
CIRCUIT DESCRIPTION
ANT
SW
RF
AMP
1st
MIX
AF
AMP
TCXO
MIC
AMP
X3
multiply
TX
AMP
PA
AMP
CF 450kHz
MCF
49.95MHz
IF SYSTEM
PLL/VCO
16.8MHz
50.4MHz
ANT
RX
TX
SP
MIC
1/2
ANT
L18
BPF
L11,13,15
BPF
Q27
RF AMP
Q13
IF AMP
IC4
AF AMP
Q15
MIX
MIX
XF1
MCF
D33,34
ANT
SW
IC8
1/2 divider
IC6
D/A
Q7
X3 multiply
X1
VCXO
IC5
MIX,IF,DET
1st local
OSC (PLL)
DEO
CF1 (Narrow)
CF2 (Wide)
APC
TUNE
CPU
Q35
Wide/
Narrow SW