TK-360G/(N)/370G/(N)
18
Fig. 3
Wide 5K/Wide 4K changeover circuit
CIRCUIT DESCRIPTION
1. Frequency configuration
The receiver utilizes double conversion. The first IF is 49.95
MHz and the second IF is 450 kHz. The first local oscillator
signal is supplied form the PLL circuit.
The PLL circuit in the transmitter generates the necessary
frequencies. Fig. 1 shows the frequencies.
Fig. 1
Frequency configuration
1) Front end (RF AMP)
The signal coming form the antenna passes through the
transmit/receive switching diode circuit, (D3,D7) passes
through a BPF, and is amplified by the RF amplifier (Q301).
The resulting signal passes through a BPF and goes to the
mixer.
2) First mixer
The signal from the front end is mixed with the first local
oscillator signal generated in the PLL circuit by Q19 to
produce a first IF frequency of 49.95 MHz.
The resulting signal passes through the XF1 MCF to cut
the adjacent spurious and provide the optimum
characteristics, such as adjacent frequency selectivity.
Fig. 2
Receiver section
ANT
TX/RX : 440~470MHz (E, (N)E)
TX/RX : 403~430MHz (E4, (N)E4)
ANT
SW
RF
AMP
PA
AMP
TX
AMP
MCF
49.95MHz
50.4MHz
CF
450kHz
IF
SYSTEM
AF
AMP
SP
RX : 390.05~420.05MHz (E, (N)E)
RX : 353.05~380.05MHz (E4, (N)E4)
16.8MHz
PLL
VCO
X3
multiply
TCXO
MIC
AMP
MIC
TX : 440~470MHz (E, (N)E)
TX : 403~430MHz (E4, (N)E4)
2. Receiver
The frequency configuration of the receiver is shown in Fig. 2.
IC4
IF, MIX, DET
AF AMP
IC16 (2/2)
X3 multiply
Q12
TCXO
5
DE-
EMP
MUTE
EXP
HPF
LPF
HPF
BEF
IC14
2
1
41
SP
AF AMP
IC11
AF AMP
IC15(2/2)
AF VOL
ANT
SW
BPF
RF
AMP
Q301
ANT
MIXER
Q19
1st Local
IF AMP
Q22
BPF
MCF
XF1
CF1 : Wide E, E4
Narrow (N)E, (N)E4
2nd Local
PLL
VCO
R75
Q23
R98
R108
C133
CD1
"H" : Wide 5K
"L" : Wide 4K
MXO
IFI
MXI
IFO
AFO
IC4
FM IF SYSTEM
Q22
5R
Wide 5K / Wide 4K
C107
R74
C108
CF1
QAD
R105
3) IF Amplifier circuit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF1) to remove the adjacent channel signal.
The filtered first IF signal is amplified by the first IF amplifier
(Q22) and then applied to the lF system IC (IC4). The IF
system IC provides a second mixer, second local oscillator,
limiting amplifier, quadrature detector and RSSI (Received
Signal Strength Indicator). The second mixer mixes the first
IF signal with the 50.4MHz of the second local oscillator
output (TCXO X3) and produces the second IF signal of
450kHz.
The second IF signal is passed through the ceramic filter
(CF1) to remove the adjacent channel signal. The filtered
second IF signal is amplified by the limiting amplifier and
demodulated by the quadrature detector with the ceramic
discriminator (CD1). The demodulated signal is routed to
the audio circuit.
4) Wide 5K/Wide 4K changeover circuit (without (N)E,
(N)E4)
The Wide 5K (high level) and Wide 4K (low level) data is
output from IC5 (OUTPUT EXPANDER), pin 4.
Q23 turns on/off with the Wide 5K/Wide 4K data and the
IC4 detector output level is changed to maintain a constant
output level during wide or narrow signals.
