Circuit Description - Kenwood 144MHz FM TRANSCEIVER K2E Service Manual

TH-K2AT/K2E/K2ET
Frequency Configuration
The frequency configuration is shown in Figure 1 and
Table 1.
RX : 136.000~173.995MHz(K,K2,M,M2)
144.000~145.995MHz(E,E3)
TX : 144.000~147.995MHz(K,K2)
136.000~173.995MHz(M,M2)
ANT
144.000~145.995MHz(E,E3)
1st MIX
RF
ANT
AMP
SW
FINAL
174.850~212.845MHz
(K,K2,M,M2)
182.850~184.845MHz
(E,E3)
PRE
DRIVE
DRIVE
144.000~147.995MHz(K,K2)
136.000~173.995MHz(M,M2)
144.000~145.995MHz(E,E3)
Fig. 1 Frequency configuration
Double super heterodyne
Reception method 1st IF Frequency
2nd IF Frequency 450kHz (Lower)
Transmission method VCO direct oscillation amplification
Modulation Variable reactance phase modulation
Table 1 Basic configuration
Receiver System
Front End
The received signal from the antenna passes through a low-
pass filter and then through a transmission/reception switching
circuit (antenna switch) and enters the band-pass filter (L40,
L41, L38).
The signal passing through the band-pass filter (L40, L41,
L38) is amplified by with an RF amplifier (Q17), passes through
a band-pass filter (L32, L35) and enters the first mixer (Q16).
These band-pass filters are tuned to a desired frequency
by varicaps (D21, D20, D19, D18).
ANT
LV
PLL
6

CIRCUIT DESCRIPTION

450kHz
CF
MCF
MIX, IF,
AF
DET AMP
38.85MHz
38.4MHz
Tripler
x 3
TCXO
PLL MIC
VCO AMP
38.85MHz (Upper)
BPF RF AMP
L41,L40,L38 Q17
ANT
LPF
SW
D21 D20
5R
VCO
6
BPF/APC
Tuning voltage
MPU
IC8
Fig. 2 Receiver section configuration
A tuning voltage corresponding to the desired signal is
applied to each varicap through the BPF/APC terminal (pin 6)
of the MPU (IC8) to tune to the receive frequency.
First Mixer
The received signal passing through the band-pass filter
(L32, L35) is mixed with the first local signal generated by the
VCO by the first mixer (Q16) to produce a first IF signal (38.85
SP
MHz) (Upper heterodyne).
The first IF signal passes through a MCF (Monolithic crystal
filter: XF1) to remove unwanted components.
The first IF signal passing through the MCF (XF1) is amplified
12.8MHz
by an IF amplifier (Q24) and the resulting signal enters the FM
MIC IC (IC3).
Item
Nominal center frequency (fo)
Pass bandwidth
Attenuation bandwidth
Ultimate attenuation
Spurious response
Ripple
Insertion loss
Terminating impedance
Table 2 MCF (L71-0619-05) characteristics (TX-RX unit XF1)
Item
Nominal center frequency (fo)
3dB bandwidth
50dB bandwidth
Ripple
Guaranteed attenuation
Insertion loss
I/O matching impedance
Table 3 Ceramic filter (L72-0968-05) characteristics (TX-RX unit CF1)
BPF MIXER MCF
L32,L35 Q16 XF1
38.85MHz
D19 D18
1st Local OSC
(PLL)
Rating
38.85MHz
±6.0kHz or more at 3dB
±25kHz or less at 35dB
70dB or more (fo –910 kHz)
40dB or more (fo +1MHz)
1dB or less
4dB or less
610Ω ±5% // 3pF ±0.5pF
Rating
450kHz
±6.5kHz or more
±15.5kHz or less
2dB or less (fo ±6.5kHz)
55dB or more
(fo ±18kHz to ±33kHz)
50dB or more (fo ±100kHz)
4dB or less
1.5kΩ
IF AMP FM IC AF AMP
Q24 IC3 IC6 SP
IF AMP,
DET
2nd Local OSC
Tripler
Q23
x 3
5R
TCXO X1
12.8MHz