Circuit Description - Kenwood TK-5810 Service Manual

TK-5810 BG
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1. Overview
This transceiver is a UHF/FM/P25 transceiver designed
to operate in the frequency range of 450 to 520MHz (K) or
400 to 470MHz (K2).
The unit consists of receiver, transmitter, phase-locked
loop (PLL) frequency synthesizer, base band parts, power
supply, and control circuits.
ANT
TX/RX: 450~520MHz (K)
TX/RX: 400~470MHz (K2)
ANT
SW
PA
AMP
3. Receiver System
3-1. Front-end RF Amplifi er
The receive signal from the RX terminal (CN200) of the
TX-RX unit (X57-727) is amplifi ed by a transistor (Q200) and
passes through the band-pass fi lter (L207, L208, L209 and
L210) to remove unwanted signal.
The signal passing through the band-pass fi lter goes into
the 1st mixer.
These band-pass fi lters are tuned to a desired frequency
by variable capacitance diode (D204, D205, D206 and D207).
1st IF
49.95MHz
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/5810H BG
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CIRCUIT DESCRIPTION

1st MIX
RF
AMP
49.95MHz
400.05~470.05MHz(K)
350.05~420.05MHz(K2)
TX
AMP 450~520MHz (K)
400~470MHz (K2)
Fig. 1 Frequency confi guration
LPF
D204,D205,D206,D207
VC
TUNE
1st MIXER
IC200
BPF
L207,L208,L209,L210
Fig. 2 Front-end RF amplifi er and 1st local
2. Frequency Confi guration
The receiver is a double-conversion superheterodyne
using fi rst intermediate frequency (IF) of 49.95MHz and sec-
ond IF of 450kHz. Incoming signals from the antenna are
mixed with the local signal from the PLL circuit to produce
the fi rst IF of 49.95MHz.
This is then mixed with the 50.4MHz second local oscil-
lator 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
amplifi ed and fed to the antenna.
CF
450kHz
MCF
MIX
IF AMP
16.8MHz
x3
VCXO
50.4MHz
PLL
VCO
A tuning voltage corresponding to the desired signal is
applied to each variable capacitance diode to tune to the re-
ceive frequency.
3-2. 1st Local
The 1st mixer uses double balanced mixer (IC200).
The receive signal passing through the band-pass fi lter
(L207, L208, L209 and L210) and the 1st local signal gener-
ated by the VCO, are mixed by the 1st mixer (IC200) to pro-
duce a 1st IF signal (49.95MHz) (Lower heterodyne).
Local AMP
Q203
VCO
RF AMP
Q200
LNA
SP
AF
AMP
ASIC
A/D
D/A
DSP
MIC
MIC
AMP
1st Local OSC
400.05~470.05MHz (K)
350.05~420.05MHz (K2
)
RX terminal (CN200)
450~520MHz (K)
400~470MHz (K2)