Circuit Description - Kenwood TK-7302 Service Manual

TK-7302/7302 V /7302H/7302H
( )
1. Frequency Confi guration
The receiver utilizes double conversion. The first IF is
38.85MHz and the second IF is 450kHz. The fi rst 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
ANT RF
SW AMP
POWER RF
AMP AMP
Fig. 1 Frequency confi guration
2. Receiver System
The receiver is a double conversion superheterodyne.
The frequency confi guration is shown in Figure 1.
2-1. Front-end RF Amplifi er
An incoming signal from the antenna is applied to an RF
amplifi er (Q506) after passing through the transmit/receive
switch circuit (D302, D303, D304 and D305) and bandpass
fi lter (L517, L518 and varactor diodes: D509, D510).
After the signal is amplifi ed (Q506), the signal is fi ltered
by the bandpass (L512, L513 and varactor diodes: D506,
D508) to eliminate unwanted signals before it is passed to
the fi rst mixer.
The voltage of these diodes are controlled by tracking
the MCU (IC702) center frequency of the bandpass filter.
(See Figure 2)
2-2. First Mixer
The signal from the RF amplifi er is heterodyned with the
fi rst local oscillator signal from the PLL frequency synthe-
sizer circuit at the fi rst mixer (Q504) to create a 38.85MHz
fi rst intermediate frequency (1st IF) signal. The fi rst IF signal
is then fed through one pair of monolithic crystal fi lters (MCF:
XF500) to further remove spurious signals.
ANT
D302,D303
D304,D305
ANT
SW
D511, L519
North filter
10
V
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CIRCUIT DESCRIPTION

CF 450kHz
MCF
38.85MHz
AF
IF SYSTEM
PA
38.4MHz
X2
multiply
19.2MHz
TCXO
RX
MIC
PLL/VCO
AMP
TX
L513,L512,L511
L517,L518 D508,D506
D509,D510 Q506 D505
BPF RF AMP BPF
TV
IC501
TVC &
DC OP AMP
APCC
Fig. 2 Receiver System
Item
Nominal center frequency
Pass bandwidth
40dB stop bandwidth
Ripple
Insertion loss
Guaranteed attenuation
SP
Terminal impedance
Table 1 Crystal fi lter (L71-0659-05): XF500
2-3. IF Amplifi er Circuit
The fi rst IF signal is amplifi ed by Q502, and enters IC500
(FM processing IC). The signal is heterodyned again with
a second local oscillator signal within IC500 to create a
MIC
450kHz second IF signal. The second IF signal is then fed
through a 450kHz ceramic filter (Wide: CF500, Narrow:
CF501) to further eliminate unwanted signals before it is
amplifi ed and demodulated by the quadrature detector with
the ceramic discriminator (CD500).
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 2 Ceramic fi lter (L72-0993-05): CF500
Item
Nominal center frequency
6dB bandwidth
50dB bandwidth
Ripple
Insertion loss
Guaranteed attenuation
Terminal impedance
Table 3 Ceramic fi lter (L72-0959-05): CF501
Q504 XF500 Q502
MIX MCF IF AMP
X1
TCXO
1st local
OSC (VCO/PLL)
Rating
38.85MHz
±6.0kHz or more at 3dB
±25.0kHz or less
1.0dB or less
4.0dB or less
75dB (–900kHz); 50dB (+900kHz)
Spurious: 40dB or more within fo±1MHz
610Ω/ 3.0pF/ Coupling Cap 13.0pF
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
CF500 (Wide)
CF501 (Narrow)
IC500 IC701
FM IC system Baseband C
Q500
Doubler
CD500