Circuit Description - Kenwood TK-360G Service Manual

TK-360G/(N)/370G/(N)
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.
TX/RX : 440~470MHz (E, (N)E)
ANT
TX/RX : 403~430MHz (E4, (N)E4)
ANT RF
AMP
SW
RX : 390.05~420.05MHz (E, (N)E)
RX : 353.05~380.05MHz (E4, (N)E4)
PA
TX
AMP AMP
TX : 440~470MHz (E, (N)E)
TX : 403~430MHz (E4, (N)E4)
Fig. 1 Frequency configuration
2. Receiver
The frequency configuration of the receiver is shown in Fig. 2.
ANT
RF
AMP
Q301
BPF
ANT
SW
CF1 : Wide E, E4
Narrow (N)E, (N)E4
IC4
IF, MIX, DET
2nd Local
X3 multiply
Q12
2 1
IC14
HPF LPF HPF
5
Fig. 2 Receiver section
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.
18

CIRCUIT DESCRIPTION

CF
450kHz
MCF
IF AF
SYSTEM AMP
49.95MHz
50.4MHz
X3
multiply
TCXO
PLL
MIC
VCO
AMP
MIXER IF AMP
MCF
XF1
BPF Q19 Q22
PLL
VCO
1st Local
AF AMP AF AMP AF AMP
IC15(2/2)
AF VOL
IC16 (2/2)
TCXO
BEF
DE-
EXP MUTE
EMP
41
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.
SP
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
16.8MHz
demodulated by the quadrature detector with the ceramic
discriminator (CD1). The demodulated signal is routed to
MIC 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.
5R
IC11
SP
AFO
Fig. 3 Wide 5K/Wide 4K changeover circuit
Q23
R105
Wide 5K / Wide 4K
Q22
IC4
FM IF SYSTEM
"H" : Wide 5K
"L" : Wide 4K
CF1