
25
TK-5710
(
B
)
/5710H
(
B
)
CIRCUIT DESCRIPTION
1. Overview
This transceiver is a VHF/FM/APCO portable transceiver
designed to operate in the frequency range of 136 to
174MHz.
Fig. 1
Frequency configuration
ANT
TX/RX : 136~174MHz
185.95~
223.95MHz
136~174MHz
PA
AMP
TX
AMP
MIC
AMP
VCXO
16.8MHz
50.4MHz
x3
ANT
SW
RF
AMP
1st MIX
49.95MHz
MCF
SP
MIC
CF
450kHz
MIX
IF AMP
PLL
VCO
FPGA
A/D
D/A
DSP
AF
AMP
The unit consists of receiver, transmitter, phase-locked
loop (PLL) frequency synthesizer, base band parts, power
supply, and control circuits.
2. Frequency Configuration
The receiver is a double-conversion superheterodyne
using first intermediate frequency (IF) of 49.95MHz and
second IF of 450kHz. Incoming signals from the antenna are
mixed with the local signal from the PLL circuit to produce
the first IF of 49.95MHz.
This is then mixed with the 50.4MHz second local
oscillator output to produce the 450kHz second IF. This
signal is detected to give the demodulated signal in the DSP.
The transmit signal frequency is generated by the PLL
VCO, and modulated by the signal from the DSP. It is then
amplified and fed to the antenna.
3. Receiver System
3-1. Front-end RF Amplifier
The receive signal from the RX terminal (CN200) of the TX-
RX unit (X57-703) is amplified by a transistor (Q200) and
passes through the band-pass filter (L221, L222, L223) to
remove unwanted signal.
The signal passing through the band-pass filter goes into
the 1st mixer.
These band-pass filters are tuned to a desired frequency
by variable capacitance diode (D200, D201, D202).
A tuning voltage corresponding to the desired signal is
applied to each variable capacitance diode to tune to the
receive frequency.
3-2. 1st Local
The 1st mixer uses double balanced mixer (A400).
The receive signal passing through the band-pass filter
(L221, L222, L223) and the 1st local signal generated by the
VCO, are mixed by the 1st mixer (A400) to produce a 1st IF
signal (49.95 MHz) (Upper heterodyne).
Fig. 2
Front-end RF amplifier and 1st local
1st IF
49.95MHz
RX terminal(CN200)
136~174MHz
1st Local OSC
185.95~223.95MHz
VC
TUNE
VCO
D200,D201,D202
RF AMP
Q200
Local AMP
Q201
BPF
L221,L222,L223
LPF
LNA
1st MIXER
A400