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NX5 OPERATION & MAINTENANCE MANUAL
DESCRIPTION
VERSION 0.1 2015-08-01
PAGE 3.1.3
Rack Interface PWB
The rack interface PWB provides various functions for the ac-dc power stage, including:
Monitors the B+ voltage and regulates the SCR rectifier’s output via the B+ level control
signal applied to the rectifier’s SCR control board.
Monitors the SCR rectifier’s temperature and phase loss indication and provides this
information, along with data received over a serial bus from the RF power modules, to the
transmitter controller.
Uses the Fast Shutback signal, if necessary, to request a transmitter shutback.
Monitors the arc detector assembly.
Generates the +30 V dc supply used by the SCR rectifier’s controller and the -15 V dc supply
used by the Hall Effect B+ current sensor
Accepts the RF drive signals from the control/interface PWB and distributes them to the power
module interface PWB.
Exciter Stage
,
and electrical schematic
SD-2
. The exciter stage
consists of digital AM exciter PWBs A (A5) and B (A6, optional) and control/interface PWB (A4). The
dual digital AM exciter PWBs provide two independent exciter sections (A and B), which can be
selected automatically or by local or remote control. The control/interface PWB acts as an interface
point for audio inputs and RF drive and PDM outputs.
Digital AM Exciter PWB(s)
The digital AM exciter PWBs [A (A5) and B (A6, optional)] accept audio signals for analog modulation,
I/Q over AES signals for DRM modulation, audio data over
I
2
S
from the audio player and IBOC signals
over
I
2
S
from an integrated Exgine card, and generate fully digital RF drive and interphase PDM drive
signals for the power amplifiers and modulators in the RF power modules.
Audio signals for analog AM modulation can be applied as balanced analog (600 ohm impedance) or
digital (AES/EBU format). All audio inputs are digitized and sample rate converted. A DSP provides
initial data conditioning, including the initial filtering and interpolation of incoming audio or digital
radio data.
An FPGA generates the digital PDM signals and synthesizes the carrier frequency RF drive signal. It also
performs digital up-conversion, reverse path demodulation and downconversion and B+ voltage
compensation.
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