Circuit Description - Kenwood TK-8102 Service Manual

TK-8102
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.
The PLL circuit in the transmitter generates the neces-
sary frequencies. Figure 1 shows the frequencies.
ANT
1st
MIX 49.95MHz
ANT RF
SW AMP
RX
POWER RF
AMP AMP
TX
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 (Q26) after passing through a transmit/receive
switch circuit (D31 and D32 are off) and a BPF (L36, L38,
L48, L49 and varactor diodes: D25, D26, D28). After the
signal is amplified (Q26), the signal is filtered by a BPF (L30,
L32 and varactor diodes: D21, D22) to eliminate unwanted
signals before it is passed to the first mixer.
The voltage of these diodes are controlled by tracking the
CPU (IC6) center frequency of the band pass filter. (See 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 (Q21) 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.
ANT
D30,31,32
ANT
SW
IC3
D/A
10

CIRCUIT DESCRIPTION

CF 450kHz
MCF
AF
IF SYSTEM
PA
50.4MHz
X3
multiply
16.8MHz
TCXO
MIC
SW
PLL/VCO
AMP
L36,38,48,49 L30,32
D25,26,28 Q26 D21,22
BPF RF AMP BPF
TV
1st local
OSC (VCO/PLL)
CPU
Fig. 2 Receiver system
IF Amplifier
The first IF signal is amplified by Q19, 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 (Wide : CF1, Narrow : CF2) to further
eliminate unwanted signals before it is amplified and FM de-
tected in IC5.
Item
Nominal center frequency
Pass bandwidth
SP
35dB stop bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 1 Crystal filter (L71-0591-05) : XF1
MIC
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 2 Ceramic filter (L72-0993-05) : CF1
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 3 Ceramic filter (L72-0994-05) : CF2
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 4 Ceramic filter (L72-0999-05) : CF2
CF1 (Wide)
CF2 (Narrow)
Q21 XF1 Q19
MIX MCF IF AMP
IF system
X1
TCXO X3 multiply
Rating
49.95MHz
± 5.0kHz or more at 3dB
± 20.0kHz or less
1.0dB or less
5.0dB or less
80dB or more at fo± 1MHz
Spurious : 40dB or more within fo± 1MHz
350Ω / 5.5pF
Rating
450kHz
± 6.0kHz or more
± 12.5kHz or less
2.0dB or less
6.0dB or less
35.0dB or more within fo± 100kHz
2.0kΩ
Rating
450kHz
± 4.5kHz or more
± 10.0kHz or less
2.0dB or less
6.0dB or less
55.0dB or more within fo± 100kHz
2.0kΩ
Rating
450kHz
± 4.5kHz or more
± 10.0kHz or less
2.0dB or less
6.0dB or less
60.0dB or more within fo± 100kHz
2.0kΩ
IC3
D/A CONVERTER
IC5
DEO
Q6