Circuit Description - Kenwood TK-8108H Service Manual

TK-8108H
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 necessary
frequencies. Figure 1 shows the frequencies.
ANT
1st
MIX 49.95MHz
ANT RF
SW AMP
POWER RF
AMP AMP
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 (Q353) after passing through a transmit/receive
switch circuit (D604 and D605 are off) and a BPF (L359, L358
L360, L361 and varactor diodes : D353, D354, D355). After
the signal is amplified (Q353), the signal is filtered by a BPF
(L354, L355 and varactor diodes: D351, D352) to eliminate
unwanted signals before it is passed to the first mixer.
The voltage of these diodes are controlled by tracking the
CPU (IC101) 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 synthesizer
circuit at the first mixer (Q352) to create a 49.95MHz first
intermediate frequency (1st IF) signal. The first IF signal is
then fed through one pair of monolithic crystal filter (MCF :
XF351) to further remove spurious signals.
ANT
D601
D602
D604
D605
ANT
SW
IC161
D/A
14

CIRCUIT DESCRIPTION

CF 450kHz
MCF
AF
IF SYSTEM
PA
50.4MHz
X3
multiply
TCXO 16.8MHz
RX
MIC
PLL/VCO
AMP
TX
L358~361 L354,355
D353~355 Q353 D351,352
BPF RF AMP BPF
TV
CPU
OSC (VCO/PLL)
Fig. 2 Receiver system
■ IF Amplifier
The first IF signal is amplified by Q351, and the enters
IC301 (FM processing IC). The signal is heterodyned again
with a second local oscillator signal within IC301 to create a
450kHz second IF signal. The second IF signal is then fed
through a 450kHz ceramic filter (Wide : CF301, Narrow :
CF302) to further eliminate unwanted signals before it is am-
plified and FM detected in IC301.
Item
SP
Nominal center frequency
Pass bandwidth
35dB stop bandwidth
Ripple
Insertion loss
Guaranteed attenMuation
MIC
Terminal impedance
Table 1 Crystal filter (L71-0591-05) : XF351
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 2 Ceramic filter (L72-0993-05) : CF301
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 3 Ceramic filter (L72-0999-05) : CF302
CF301 (Wide)
CF302 (Narrow)
Q352 XF351 Q351
MIX MCF IF AMP
X401
TCXO
1st local
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
60.0dB or more within fo± 100kHz
2.0kΩ
IC161
D/A CONVERTER
IC301
IF system
W/NO
(EVOL2)
Q302
X3 multiply