Circuit Description - Kenwood NX-411 Service Manual

NX-411
1. Overview
The NX-411 is an 900MHz Portable transceiver designed
to operate in the frequency range of 896 to 941MHz.
The unit consists of receiver, transmitter, phase-locked
loop (PLL) frequency synthesizer, baseband parts, power
supply, and control circuits.
3. Receiver System
3-1. RF Circuit
An incoming RF signal from the antenna terminal is
passed through the antenna switch (D605, D606, D607 and
D608) and then the band-pass fi lter (L830).
The signal is amplifi ed by an RF amplifi er (Q804), and
passed through the band-pass filter (L820). The resulting
signal is applied to the fi rst mixer (IC804), where it is mixed
with the fi rst local oscillator signal output from the frequency
synthesizer to produce the fi rst IF (58.05MHz).
3-2. IF Circuit
The fi rst IF signal is passed through a four-pole mono-
D605, D606
D607, D608 L830
ANT
BPF
SW
12

CIRCUIT DESCRIPTION

ANT 896~902MHz (TX)
935~941MHz (RX/TX)
1st Mixer
ANT
LNA
SW
58.05MHz
993.05~
999.05MHz
19.2MHz
PA TX TX/RX
AMP AMP SW
896~902MHz
935~941MHz
Fig. 1 Frequency confi guration
Q804 L820 IC804
1st
LNA BPF
Mixer
1st Lo
Fig. 2 RF and IF circuit
2. Frequency Confi guration
The receiver is a double-conversion superheterodyne us-
ing the fi rst intermediate frequency (IF) of 58.05MHz and the
second 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 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 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
2nd Mixer
MCF
IF AMP
ASIC
x3
A/D
D/A
TCXO
DSP
PLL
VCO
lithic crystal fi lter (XF801) to reject adjacent channel signals.
The fi ltered fi rst IF signal is amplifi ed by the fi rst IF amplifi er
(Q802) and then applied to the lF system IC (IC802). The
IF system IC provides a second mixer, AGC amplifi er, and
RSSI (Received Signal Strength Indicator).
The second mixer mixes the first IF signal with the
57.6MHz of the second local oscillator output and produces
the second IF signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
(CF801) to reject the adjacent channel signal. The fi ltered
second IF signal is amplifi ed by the AGC amplifi er.
The signal from the AGC amplifi er is input to the ASIC
(IC309) through the ceramic fi lter (CF802) and operational
amplifi er (IC801).
CF801
XF801 Q802
IF
BPF
AMP
X501 Q801
AMP
TCXO
(x3)
SP
AF
AMP
MIC
MIC
AMP
BPF
IC802 CF802 IC801
FM IC BPF AMP
IC309
ASIC