Circuit Description - Kenwood TK-7160 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
1/2
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 Circuit
An incoming signal from the antenna is applied to an RF
amplifier (Q353) after passing through a transmit/receive
switch circuit (D602 and D603 are off) and a band pass filter
(L357, L356 and varactor diodes : D353, D354). After the
signal is amplified (Q353), the signal is filtered through a band
pass filter (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 Circuit
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 a monolithic crystal filter (MCF : XF351) to
further remove spurious signals.
ANT
L357,356
D602 D353,354
D603
ANT
SW
IC201
D/A

CIRCUIT DESCRIPTION

CF 450kHz
AF
IF SYSTEM SP
PA
50.4MHz
X3
multiply
16.8MHz
TCXO
MIC
PLL/VCO MIC
AMP
L354,355
Q353 Q352
D351,352
BPF RF AMP BPF MIX
IC402
TV
1/2 divider
CPU
1st local
OSC (VCO/PLL)
Fig. 2 Receiver system
TK-7160/7162
■ IF Amplifier Circuit
The first IF signal is amplified by Q351, and the enters
IC321 (FM processing IC). The signal is heterodyned again
with a second local oscillator signal within IC321 to create a
450kHz second IF signal. The second IF signal is then fed
through a 450kHz ceramic filter (Wide : CF331, Narrow :
CF332) to further eliminate unwanted signals before it is am-
plified and FM detected in IC321.
Item
Nominal center frequency
Pass bandwidth
35dB stop bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 1 Crystal filter (L71-0624-05) : XF351
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 2 Ceramic filter (L72-0993-05) : CF331
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 3 Ceramic filter (L72-0999-05) : CF332
CF331 (Wide)
CF332 (Narrow)
XF351 Q351
MCF IF AMP
IC321
IF system
X401 Q341
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
60.0dB or more within fo± 100kHz
2.0kΩ
IC201
D/A CONVERTER
W/NO
11