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NXR-901
1. Outline
The NXR-901 is a UHF repeater operating at 896 to
902MHz for receiving and 935 to 941MHz for transmitting.
The 896 to 901MHz/935 to 940MHz band is defi ned by
47CFR Part 90. In this band, transmit frequency accuracy
is required to be +/-0.1ppm. The 901 to 902MHz/940 to
941MHz band is defined by 47CFR Part 24. In this band,
transmit frequency accuracy is required to be +/-1.0ppm. For
good communication quality in the NXDN system, it is rec-
ommended that frequency accuracy is smaller than or equal
to +/-0.5ppm.
The receiver part of the NXR-901 is confi gured as dou-
ble-conversion super heterodyne. The 1st IF is 73.05MHz
and the 2nd IF is 450kHz.
The IF system IC for Analog mode demodulates the FM
IF signal into an audio signal. The audio signal is fed to the
DSP to process fi ltering.
The IF system IC for Digital mode converts the 1st IF
signal to the 2nd IF and the signal level is controlled by the
AGC function. The levelled 2nd IF signal is fed to the DSP to
process additional fi ltering and demodulation.
The transmitter part of the NXR-901 is confi gured to di-
rect VCO modulation. To have a wide range modulation fre-
quency band, 19.2MHz modulator PLL can be modulated by
near DC to 100~200Hz signal.
The NXR-901 has a 10.0MHz reference signal distribu-
tion circuit. The internal 20.0MHz PLL is phase locked with
the "REF IN" external 10.0MHz reference signal, the internal
19.2MHz TCXO signal (is converted to 5.99MHz) or the op-
tional OCXO's 10.0MHz signal. The locked 20.0MHz signal
is divided by 2, then the 10.0MHz signal is fed to the "REF
OUT" terminal to synchronize the other repeaters.
TX UNIT
CN403
LPF
REF_OUT
CVT_REF
CN408
LPF
REF_IN
Q511
CN407
OCXO
19.2MHz
X401
8
CIRCUIT DESCRIPTION
10.0MHz
LPF
1/2
Q503
Q506
IC503
20.0MHz
BUFF
LPF
IC302
X301
IC303
PLL IC
LPF
SW
D516,D517
Q505
Q504
D518,D519
BUFF
DDS
IC402
IC401
Q402
Fig. 1 Internal/external reference circuit and 20.0MHz PLL circuit
2. Transmitter Unit
The Transmitter unit (X56-315 A/3) consists of the follow-
ing circuit.
(1) Internal/external reference circuit
(2) Internal frequency reference 20.0MHz PLL circuit and 1/2
divider
(3) Transmitter Modulation 19.2MHz PLL circuit
(4) Transmitter main PLL circuit
(5) Driver circuit
(6) Modulation level adjustment circuit
(7) AVR circuits
(8) Other circuits
2-1. Internal/external reference circuit
The internal TCXO X401 (19.2MHz) is the frequency
reference for the TX, RX and Control units. The internal
20.0MHz PLL circuit (X301 and IC303) is locked from this
signal (frequency is converted from 19.2MHz to 5.99MHz
by the DDS IC, IC401). The 20.0MHz signal is distributed
to the TX, RX and Control units. In addition, the 20.0MHz
signal is divided by 2 to generate 10.0MHz. This 10.0MHz
signal is distributed by the "REF OUT" terminal to the other
NXR-901s to synchronize the RX/TX frequency.
The NXR-901 can operate with one of the follow-
ing frequency reference signals, the internal TCXO X401
(19.2MHz), external reference signal (10.0MHz) from "REF
IN", and optional OCXO unit KXK-3 (M3) (10.0MHz).
The internal/external reference circuit automatically
switches signals used as reference signals among the
5.99MHz internal DDS (generated by 19.2MHz, X401), the
10MHz external reference signal and the 10MHz OCXO unit.
If no OCXO unit is installed, and there is no external
BUFF
LPF
IC504
Q514
LPF
Q307
Q308
Q306
BUFF
10.0MHz
IC301
LPF
SW
D401,D402
D503,D507
LPF
BPF
CF401
TX Mod 19.2MHz
LPF
PLL circuit
Q309
LPF
Control unit
Q310
RX unit
LPF
Q311
5.99MHz
LPF
Q401
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