Circuit Description - Kenwood TK-8102H Service Manual

TK-8102H
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 (D803 and D804 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.
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.
10

CIRCUIT DESCRIPTION

CF 450kHz
MCF
AF
IF SYSTEM
PA
50.4MHz
X3
multiply
TCXO 16.8MHz
MIC
1/2
PLL/VCO
AMP
Item
Nominal center frequency
Pass bandwidth
35dB stop bandwidth
Ripple
Insertion loss
Guaranteed attenMuation
Terminal impedance
SP
Table 1 Crystal filter (L71-0591-05) : XF1
Item
Nominal center frequency
6dB bandwidth
MIC
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 (L72-0999-05) : CF2
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
350 / 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
2.0k
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
2.0k