TK-3140
6
CIRCUIT DESCRIPTION
1. Overview
This transceiver is UHF/FM portable transceiver designed to
operate in the frequency range of 450 to 490MHz (K) and an UHF/
FM band EFJ LTR
TM
trunked system compatible FM portable
transceiver 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.
ANT
TX/RX : 450~490MHz : K
ANT
SW
RF
AMP
PA
AMP
TX
AMP
1st MIX
MCF
44.85MHz
CF
455kHz
FM IF
SYSTEM
AF
AMP
SP
44.395MHz
405.15~445.15MHz : K
PLL
VCO
MIC
AMP
MIC
450~490MHz : K
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 (D102, D103, D104. and D105 are
off) and then the bandpass filter (L215,217). High pass filter
HPF (L219) the 1st image response improve. And 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 (IC307). The signal is amplified by RF
amplifier Q207, and passed through the bandpass filter
(L209,210,211). The resulting signal is applied to the first mixer
(Q206), where it is mixed with the first local oscillator signal
output from the frequency synthesizer to produce the first IF
(44.85MHz).
3-2. IF unit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF200) to remove a adjacent channel signal. The
filtered first IF signal is amplified by the first IF amplifier (Q205)
and then applied to the lF system IC (IC200). 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 X200) and produces the second IF signal of 455kHz.
The second IF signal is passed through the ceramic filter
(CF200; Wide, CF201 ; Narrow) to more remove the adjacent
channel signal. The filtered second IF signal is amplified by
the limiting amplifier and demodulated by the quadrature
detector with ceramic discriminator (CD200). The demodulated
signal is routed to the audio circuit.
Fig. 2
Receiver section
IC200
MIX, DET, IF
SW
Q204
DM
DM
IC300 (2/2)
AF AMP
5
DE-
EMP
MUTE
EXP
HPF
LPF
HPF
BEF
IC500
2
1
VOL
IC307
IC305 (2/2)
AF AMP
41
VC1
VC2
Q308
SSW
INT.
SP
EXT.
SP
2nd local
OSC
X200
SW
IC313
AF PA
ANT
SW
L110,111
L112
L215,217
BPF
D102,103
D104,105
Q207
RF
AMP
ANT
Q206
1st MIX
Q205
1st IF
L209,210
L211
BPF
XF200
MCF
1st Local
OSC (PLL)
CF200 : Wide
CF201 : Narrow
Center Frequency
Nominal 455kHz
Band Width
3dB
Min.
±
6.5kHz
50dB
Max.
±
15.5kHz
Stop Band Attenuation
±
18~
±
33kHz
Min. 55.0dB
±
100kHz
Min. 50.0dB
Spurious Response
0.1~1.0MHz
Min. 20.0dB
Ripple
Within 455
±
6.5kHz
Max. 2.0dB
Insertion Loss
at 455 kHz
Max. 4.0dB
Group Delay Time
Within 455
±
3.0kHz
Max. 25.0
µ
sec
Within 455
±
5.0kHz
Max. 50.0
µ
sec
Table 1
Ceramic filter (L72-0995-05): CF200
