Circuit Description - Kenwood TH-K40A Service Manual

TH-K40A/K40E
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 os-
cillator is supplied from the PLL circuit.
RX: 400~469.995MHz(M,E)
TX: 400~469.995MHz(M)
ANT
ANT
SW
TX: 400~469.995MHz(M)
TX
AMP
2. Receiver System
The receiver system is shown in Figure 2.
2-1. RF Amplifi er Circuit
The signal coming from the antenna passes through the
transmit/receive switching diode circuit (D101, D102, D103
and D104) and a BPF (L212, L213), and is then amplifi ed by
the RF amplifi er (Q204).
The resulting signal passes through a BPF (L209, L210,
L211 and L217) and goes to the mixer. These BPFs are ad-
justed by variable capacitors (D200, D201, D202, D203 and
D204). The input voltage to the variable capacitor is a regu-
lated voltage output from the DAC (IC300).
2-2. First Mixer
The signal from the front end is mixed with the fi rst local
oscillator signal generated in the PLL circuit by Q203 to pro-
duce a fi rst IF frequency of 38.85 MHz.
The resulting signal passes through the XF200 MCF to
cut the adjacent spurious and provide the optimum charac-
teristics, such as adjacent frequency selectivity.
ANT
BPF
ANT
SW
BPF
4

CIRCUIT DESCRIPTION

430~439.995MHz(E)
1st MIX MCF
RF
AMP
38.85MHz
1st Lo:
361.150~
431.145MHz
430~439.995MHz(E)
Fig. 1 Frequency confi guration
Q204 Q203
RF AMP BPF 1st MIX
BPF 1st Local
Fig. 2 Receiver system
The PLL circuit in the transmitter generates the neces-
sary frequencies.
CF
450kHz
IF AF
SYSTEM
filter
38.4MHz
X2
TCXO
doubler
PLL
T/R
RF
VCO
SW AMP
Item
Nominal center frequency (fo)
Pass bandwidth
Attenuation bandwidth
Ultimate attenuation
Spurious response
Ripple
Insertion loss
Terminating impedanc
MCF (L71-0669-05) characteristics (TX-RX unit XF200)
Item
Nominal center frequency (fo)
3dB bandwidth
50dB bandwidth
Ripple
Guaranteed attenuation
Insertion loss
I/O matching impedance
Ceramic filter (L72-1042-05) characteristics (TX-RX unit CF200)
CF200
Q202
XF200 IF AMP
IC200
IF,MIX,DET
MCF
2nd Local
Q201
doubler
SP
AF
AMP
19.2MHz
MIC
MIC
AMP
Rating
38.850MHz
±5.0kHz or more at 3dB
±25.0kHz or less at 45dB
70dB or more (fo –900 kHz)
40dB or more (fo +1MHz)
1dB or less
5dB or less
610 // 3pF
Rating
450kHz
±4.5kHz or more
±11.0kHz or less
2dB or less (
50dB or more (fo
6dB or less
1.5k
IC303
IC307
AF filter
VR300 AF PA
X1
TCXO
19.2MHz
o f ± 3.0kHz)
100kHz)
±
SP