Circuit Description - Kenwood TK-380 Service Manual

TK-380
1. Overview
This transceiver is UHF/FM portable transceiver designed to
operate in the frequency range of 450 to 490MHz (F1), 470 to
512MHz (F2), 400 to 430MHz (F3) and an UHF/FM band EFJ LTR
trunked system compatible FM portable transceive that can be
programmed to operate on both LTR and conventional systems.
2. Circuit Configuration by Frequency
The receiver is a double-conversion superheterodyne with
a first intermediate frequency (IF) of 44.85MHz and a second
IF of 455kHz. Incoming signals from the antenna are mixed
with the local signal from the PLL to produce the first IF of
44.85MHz.
This is then mixed with the 44.395MHz second local
oscillator output to produce the 455kHz second IF. This is
detected to give the demodulated signal.
The transmit signal frequency is generated by the PLL VCO,
and modulated by the signal from the microphone. It is then
amplified and sent to the antenna.
TX/RX : 450~490MHz : K, K4, M
470~512MHz : K2, K5
ANT
400~430MHz : K3, K6, M3
1st MIX
ANT RF
SW AMP
44.85MHz
355.15~385.15MHz : K3, K6, M3
425.15~467.15MHz : K2, K5
405.15~445.15MHz : K, K4, M
PA TX
AMP
AMP
450~490MHz : K, K4, M
470~512MHz : K2, K5
400~430MHz : K3, K6, M3
Fig. 1 Frequency configuration
3. Receiver System
3-1. RF unit
An incoming RF signal from the antenna terminal is passed
through the antenna switch (D12, D14. and D15 are off) and
ANT
L47,48,
49,51,
52,54,
L40,42, D12
55,56
43 D14,15
BPF
ANT
SW
2
IC13
HPF LPF
5
16

CIRCUIT DESCRIPTION

CF
455kHz
MCF
FM IF AF
SYSTEM
AMP
44.395MHz
PLL
MIC
VCO
AMP
Q24
L29,31,
IC18
RF
33,34,36 L27
AMP BPF BEF 1st MIX
1st Local
OSC (PLL)
1
HPF BEF
DE-
EXP
EMP
Fig. 2 Receiver section
then the bandpass filter (L47,48,49,51,52,54,55,56). The
bandpass filter is adjusted by a variable capacitor. The input
voltage to the variable capacitor is regulated by the voltage
output from the D/A converter (IC8). The signal is amplified by
TM
RF amplifier Q24, and passed through the bandpass filter
(L29,31,33,34,36) and band-eliminate filter (L27) to remove
the spurious signal again. The resulting signal is applied to the
first mixer (IC18), where it is mixed with the first local oscillator
signal output from the frequency synthesizer to produce the
first IF (44.85MHz). The 1st mixer uses the GaAs IC.
3-2. IF unit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF1) to remove a adjacent channel signal. The
filtered first IF signal is amplified by the first IF amplifier (Q12)
and then applied to the lF system IC (IC12). 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 44.395MHz of second local oscillator output (crystal
unit X2) and produces the second IF signal of 455kHz.
The second IF signal is passed through the ceramic filter
(CF1; Wide, CF2 ; Narrow) to more remove the adjacent
channel signal. The filtered second IF signal is amplified by
SP
the limiting amplifier and demodulated by the quadrature
detector with ceramic discriminator (CD1). The demodulated
signal is routed to the audio circuit.
3-3. Wide/Narrow changeover circuit
MIC
Narrow and Wide settings can be made for each channel
by switching the ceramic filters CF1 (Wide), CF2 (Narrow).
The WIDE (high level) and NARROW (low level) data is
output from IC19 (microconputer) pin 99.
When a WIDE (high level) data is received, Q6 turn off and
Q7 turn on. When a NARROW (low level) data is received,
Q6 turn on and Q7 turn off. D5, D7 are switched to ceramic
filters when a high/low level data is received.
Q9 turns on/off with the Wide/Narrow data and the IC12
detector output level is changed to maintain a constant output
level during wide or narrow signals.
Q12
XF1
MCF
1st IF
IC12
MIX, DET, IF
X2
2nd local
OSC
IC7 (2/2)
AF AMP IC8
MUTE
VOL
41
IC4 (2/2)
AF AMP
Q15
SW
CF1 : Wide
DM DM
CF2 : Narrow
IC300
AF PA
Q310
AF AF
SW
VC1
SSW
VC2
INT.
SP
EXT.
SP