TH-K2AT/K2E/K2ET
6
CIRCUIT DESCRIPTION
Frequency Configuration
The f requency conf igurat ion is show n in Figure 1 and
Table 1.
Fig. 1 Frequency configuration
174.850~212.845M Hz
(K,K2,M ,M 2)
182.850~184.845M Hz
(E,E3)
144.000~147.995M Hz(K,K2)
136.000~173.995M Hz(M ,M 2)
144.000~145.995M Hz(E,E3)
136.000~173.995M Hz(K,K2,M ,M 2)
144.000~145.995M Hz(E,E3)
144.000~147.995M Hz(K,K2)
136.000~173.995M Hz(M ,M 2)
144.000~145.995M Hz(E,E3)
RX :
TX :
ANT
SW
M CF
38.85M Hz
38.4M Hz
12.8M Hz
450kHz
CF
M IX, IF,
DET
AF
AM P
SP
PRE
DRIVE
FINAL
TCXO
DRIVE
Tripler
x 3
RF
AM P
1st M IX
PLL
VCO
M IC
AM P
M IC
ANT
Receiver System
■
Front End
The received signal from the antenna passes through a low -
pass filter and then through a transmission/reception sw itching
circuit (antenna sw itch) and enters the band-pass filter (L40,
L41, L38).
The signal passing through the band-pass filter (L40, L41,
L38) is amplified by w ith 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).
Double super heterodyne
Reception method
1st IF Frequency
38.85M Hz (Upper)
2nd IF Frequency 450kHz (Low er)
Transmission method VCO direct oscillation amplification
M odulation
Variable reactance phase modulation
Table 1 Basic configuration
ANT
SW
SP
LPF
VCO
BPF/APC
M PU
IC8
PLL
IF AM P,
DET
Tripler
x 3
TCXO
BPF
L41,L40,L38
BPF
L32,L35
M IXER
Q16
1st Local OSC
(PLL)
RF AM P
Q17
ANT
M CF
XF1
IF AM P
Q24
FM IC
IC3
Q23
2nd Local OSC
X1
AF AM P
IC6
5R
5R
D20
D21
LV
6
Tuning voltage
D18
38.85M Hz
12.8M Hz
D19
A tuning voltage corresponding to the desired signal is
applied to each varicap through the BPF/APC terminal (pin 6)
of the M PU (IC8) to tune to the receive frequency.
■
First M ixer
The received signal passing through the band-pass filter
(L32, L35) is mixed w ith the first local signal generated by the
VCO by the first mixer (Q16) to produce a first IF signal (38.85
M Hz) (Upper heterodyne).
The first IF signal passes through a M CF (M onolithic crystal
filter: XF1) to remove unw anted components.
The first IF signal passing through the M CF (XF1) is amplified
by an IF amplifier (Q24) and the resulting signal enters the FM
IC (IC3).
Fig. 2 Receiver section configuration
Item
Rating
Nominal center frequency (fo)
38.85M Hz
Pass bandw idth
±6.0kHz or more at 3dB
Attenuation bandw idth
±25kHz or less at 35dB
Ultimate attenuation
70dB or more (fo –910 kHz)
Spurious response
40dB or more (fo +1M Hz)
Ripple
1dB or less
Insertion loss
4dB or less
Terminating impedance
610
Ω
±5% // 3pF ±0.5pF
Table 2 MCF (L71-0619-05) characteristics (TX-RX unit XF1)
Item
Rating
Nominal center frequency (fo)
450kHz
3dB bandw idth
±6.5kHz or more
50dB bandw idth
±15.5kHz or less
Ripple
2dB or less (fo ±6.5kHz)
55dB or more
Guaranteed attenuation
(fo ±18kHz to ±33kHz)
50dB or more (fo ±100kHz)
Insertion loss
4dB or less
I/O matching impedance
1.5k
Ω
Table 3 Ceramic filter (L72-0968-05) characteristics (TX-RX unit CF1)