(No.RA075<Rev.001>)1-19
2.4
CIRCUIT DESCRIPTION
2.4.1 Overview
The NX-5600HB is a Low Band Analog FM & Digital Mobile transceiver designed to operate in the frequency range of 39 to 50MHz.
The unit consists of a receiver, a transmitter, a phase-locked loop (PLL) frequency synthesizer, a digital control unit, and a power
supply circuit.
2.4.2 Frequency Configuration
The receiver is a double-conversion super-heterodyne using first intermediate frequency (IF) of 10.70MHz and second IF of 2.10MHz.
Incoming signals from the antenna are mixed with the local signal from the VCO/PLL circuit to produce the first IF of 10.70MHz. This
is then mixed with the 12.80MHz second local oscillator output to produce the 2.10MHz second IF. The transmit signal frequency is
generated by the PLL and the VCO-B, and modulated by the signal from the Baseband Circuit. It is then amplified and fed to the
antenna.
Fig.1 Frequency configuration
2.4.3 Receiver System
2.4.3.1
RF Circuit
The receive signal from antenna switch (D306, D307, D308, D309 and D310) is amplified by a RF amplifier (Q505) and passes through
the band-pass filter (L503, L510, L511, L512, L516, L521, L524, L526, L527 and L531) to remove unwanted signals. The signal is
then fed to the 1st mixer (Q502, Q503, Q504 and Q514).
2.4.3.2
IF Circuit
Since there is a noise blanker circuit in the IF circuit section, the IF signal first passes through the delay circuit.
When the noise blanker function is effective, noise is suppressed.
The first IF signal then passed through a four-pole monolithic crystal filter (XF601) to reject adjacent channel signal. The filtered first
IF signal is amplified by the first IF amplifier (Q604 and Q603) and then applied to the IF system IC (IC600). The IF system IC provides
a second mixer, second PLL, AGC and A/D converter.
The second mixer mixes the first IF signal with the 12.80MHz of second local oscillator output and produces the second IF signal of
2.10MHz.
The second IF signal is then be fed into an A/D converter, generates the “I” and “Q” data. This data is in the form of SSI (Serial
Synchronous Interface), and sent to the MPU/DSP (IC706).
2.4.3.3
Audio Amplifier Circuit
Audio processing (high-pass filter, low-pass filter, de-emphasized and so on) at Analog FM mode and decoding at Digital mode are
processed by DSP. SSI signal from DSP is converted to audio signal at CODEC (IC902). The signal goes to connector for external
speaker (CN9) through the amplifier (IC903), electronic volume control (IC719), the amplifier (IC906), Changeover switch (IC912) and
audio amplifier (IC911).
Fig.2 RF and IF circuit
ANT
EXT SP
12.80MHz
10.70MHz
19.2MHz
230.4~314.4MHz
312~401.6MHzMHz
39~50MHz
28.8
〜
39.3MHz
49.7
〜
50.2MHz
X
I
M
t
s
1
MIC
ANT
SW
PA
AMP
RF
AMP
TX
AMP
MCF
MIX
IF Circuit
SW
PLL
TCXO
VCO-A
VCO-B
1/8
2nd
VCO
Baseband
Circuit
CODEC
AF
AMP
TX/RX: 39~50MHz
ANT
D306
Q600
D307,308
Q505
L503,510
L511,512
L516
D309,310
L521,524
L526,527
L531
RF AMP
SSI
IC600
IF AMP
IF AMP
MCF
RX VCO/PLL
IC903
IC719
IC906
IC706
IC902
External Speaker
ANT
LPF
ANT
SW
BPF
BPF
BPF
Delay
Circuit
Noise
Blanker
NB
SW
IF IC
2nd
VCO
MPU/DSP
CODEC
IC911
CN9
VOL
IC912
SW
Q502,503
Q504,514
XF601
Q606,607
Q608
IF AMP
Q604
Q603
Содержание NX-5600HB
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