Circuit Description - Kenwood NX-800H Service Manual

1. Overview
NX-800/800H is a UHF Mobile transceiver designed to
operate in the frequency range of 450 to 520MHz. The unit
consists of receiver, transmitter, phase-locked loop (PLL)
frequency synthesizer, base band parts, power supply, and
control circuits.
ANT
ANT
SW
PA
AMP
3. Receiver System
3-1. RF circuit
The front-end circuit consists of former BPF (D212,
D213), RF amplifier Q210, and latter BPF (D207, D208,
D209 and D210).
The BPF covers frequency ranges 450 to 520MHz.
The latter BPF (D207, D208, D209 and D210) attenuates
the unwanted signals, and sends only the necessary signal
to the fi rst mixer.
–118dBm –120.5dBm
ANT
D212,D213
BPF
Buff AMP
Q9
RX
VCO

CIRCUIT DESCRIPTION

TX/RX: 450~520MHz
1st MIX MCF
RF
AMP
58.05MHz
19.2MHz
VCTCXO
391.95~
461.95MHz
TX
AMP
450~520MHz
Fig. 1 Frequency confi guration
–114.5dBm
RF AMP D207~
1st MIX DBM
Q210 D210
BPF
Buff AMP Buff AMP
Q10 Q208
BPF
0dBm
NX-800/800H
2. Frequency Confi guration
The receiver is a double-conversion super heterodyne
using first intermediate frequency (IF) of 58.05MHz and
second IF of 450kHz. Incoming signals from the antenna
are mixed with the local signal from the PLL circuit to pro-
duce the first IF of 58.05MHz. This is then mixed with
the 57.6MHz second local oscillator output to produce the
450kHz second IF. The transmit signal frequency is gener-
ated by the PLL VCO, and modulated by the signal from the
DSP. It is then amplifi ed and fed to the antenna.
CF
450kHz
MIX
IF AMP
x3
57.6MHz
PLL
VCO
3-2. First Mixer
The signal from the BPF is heterodyned with the fi rst lo-
cal oscillator signal from the PLL frequency synthesizer cir-
cuit at the fi rst mixer DBM (IC204) to become a 58.05MHz
fi rst intermediate frequency (IF) signal.
The fi rst IF signal is fed through a monolithic crystal fi lter
(XF202) to further remove spurious signals.
–112.5dBm
IF AMP
Q205
XF202
IC204
MCF
0dBm
Fig. 2
SP
AF
AMP
MIC
MIC
AMP
–104dBm
IF AMP FM SYSTEM IC
Q204 IC202
17