Circuit Description - Kenwood TK-8100H Service Manual

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 MCF
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 (Q353) after passing through a transmit/receive
switch circuit (D604 and D603 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
L358~361
D601~ D353~355
D604
ANT
SW
IC161
D/A

CIRCUIT DESCRIPTION

CF 450kHz
AF
IF SYSTEM SP
PA
50.4MHz
X3
multiply
TCXO 16.8MHz
MIC
PLL/VCO MIC
AMP
L354,355
Q353 D351,352 Q352
BPF RF AMP BPF MIX
TV
1st local
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
Nominal center frequency
Pass bandwidth
35dB stop bandwidth
Ripple
Insertion loss
Guaranteed attenMuation
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)
XF351 Q351
MCF IF AMP
IC301
IF system
X401 Q302
TCXO X3 multiply
TK-8100H
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
W/NO
(EVOL2)
15