Circuit Description; Frequency Configuration; Receiver System; First Mixer - Kenwood TK-7360 Service Manual

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 MCF
MIX 38.85MHz
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 (Q511) after passing through the transmit/receive
switch circuit (D303, D304, D307 and D308) and bandpass
fi lter (L518, L519 and varactor diodes: D506, D507).
After the signal is amplifi ed (Q511), the signal is fi ltered
by the bandpass (L513 and varactor diodes: D504, D505) to
eliminate unwanted signals before it is passed to the fi rst
mixer.
The voltage of these diodes are controlled by tracking
the MCU (IC704) 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 (Q507) 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
L518,L519
D303,D304 D506,D507
D307,D308
BPF
ANT
SW
IC501
DC OP AMP

CIRCUIT DESCRIPTION

CF 450kHz
SP
AF
IF SYSTEM
PA
38.4MHz
X2
multiply
19.2MHz
TCXO
MIC
RX
MIC
PLL/VCO
AMP
TX
L513
D504,D505
Q511 Q507
RF AMP BPF
TV
1st local
TVC &
OSC (VCO/PLL)
APCC
Fig. 2 Receiver System
TK-7360/7360H/7360H
Item
Nominal center frequency
Pass bandwidth
40dB stop bandwidth
Ripple
Insertion loss
Guaranteed attenuation
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 Q504, and enters IC500
(FM processing IC). The signal is heterodyned again with
a second local oscillator signal within IC500 to create a
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 (L72-0999-05): CF501
CF501 (Narrow)
XF500 Q504
MIX MCF IF AMP
X1 Q500
TCXO Doubler
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)
IC500 IC702
FM system IC Baseband IC
CD500
V
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