Circuit Description - Kenwood UBZ-LJ8 Service Manual

UBZ-LJ8
Frequency Configuration
ANT
Simplex
446.00625~446.09375MHz
LPF
BPF
446MHz
ANT RF
SW AMP
RF RF RF
AMP AMP AMP
Fig. 1 Frequency configuration
Reception method
Transmission method
Modulation
Receiver System
■ Front End
The high-frequency signal received from antenna passes
through a LPF (Low pass filter : components between ANT
and C73) to filter out unwanted high frequency signal. A
switch diode system (D8, L32 and D10) allows this signal to
pass through and enters the BPF (Band pass filter : L31) to
eliminate unwanted signal when receiving.
The resulting signal is amplified by high-frequency ampli-
fier (Q9) and goes to the first mixer (Q10).
■ First Mixer
The amplified signal that reaches Q10 is mixed with the
first local signal from a VCO to produce a first IF signal
(21.7MHz).
(Receive frequency – First local frequency
= First IF frequency = 21.7MHz)
The first IF signal passes through MCF (Monolithic crystal
filter) XF1 to eliminate unwanted components.
The first IF signal is amplified by IF amplifier (Q11) before
going into FM IC (IC2).
ANT
2

CIRCUIT DESCRIPTION

21.7MHz
1st MIX MCF
AF
MIX, IF
DET AMP
Simplex
21.25MHz
424.30625~
424.39375MHz
PLL
MIC
VCO
AMP
Simplex
446.00625~
446.09375MHz
21.25MHz
TCXO
Double super heterodyne
1st IF frequency 21.7MHz (Lower)
2nd IF frequency 450kHz (Lower)
VCO direct amplification
Variable reactance phase modulation
Table 1
D8,D10 BPF
LPF L32 L31
ANT
SW
446MHz
Fig. 2 Receiver section configuration
ANT
LPF
SP
1st local
OSC
VCO
MIC
Q10
Fig. 3 Receiver front end and Mixer circuit
Nominal center frequency (fo)
Pass bandwidth
Attenuation bandwidth
Ripple
Insertion loss
Ultimate attenuation
Spurious responses
Terminating impedance
Table 2 MCF (L71-0616-05) : TX-RX Unit XF1
Nominal center frequency (fo)
6dB bandwidth
50dB bandwidth
Ripple (450kHz ± 3kHz)
Guaranteed attenuation (± 100kHz)
Insertion loss
I/O matching impedance
Table 3 Ceramic filter (L72-0974-05) : TX-RX Unit CF1
1st MIX MCF IF AMP
RF AMP
Q10 XF1 Q11
Q9
21.7MHz
1st local OSC (PLL)
3T 3R
Q9
L31
L32
XF1
Q11
3R
Item
21.7MHz
± 3.75kHz or more at 3dB
± 14kHz or less at 40dB
1dB or less
3.5dB or less
80dB or more (fo ± 910kHz)
40dB or more (fo ± 1MHz)
850Ω± 5% // 5pF± 0.5pF
Item
450kHz
± 4.5kHz or more
± 10kHz or less
3dB or less
40dB or more
4dB or less
2.0kΩ± 10%
FM IC AF AMP
IC2 IC203
SP
MIX,
DET
2nd local OSC
FM IC
3R
Rating
Rating