NX15/NX25 Operations and Maintenance Manual
Description
Page 1-4
Issue 6.0 2019-01-31
Exciter Stage
See
and electrical schematic
SD-2
. The exciter stage consists of digital AM exciter
PWBs A (A11A2) and B (A11A3), RF drive distribution PWB (A7), and PDM distribution
PWB (A8). 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 PWBs
Digital AM exciter PWBs A (A11A2) and B (A11A3) accept audio signals for analog
modulation, I/Q over AES signals for DRM modulation and IBOC signals over I2S 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 down-conversion
and B+ voltage compensation.
Figure 1.1: Exciter Stage
Digital AM
Exciter A
+15 V dc
-15 V dc
+5 V dc
Analog/
Digital
Modulation
Inputs
Digital AM
Exciter B
Co
ntr
ol/In
terf
ace
Analog/
Digital Mod-
ulation
Inputs
Con
tro
l/Int
erface
RF Drive (A)
RF Drive (B)
PDM (A)
PDM (B)
RF Drive 1
RF Drive 2
PDM 2/5/8
To RF Po
wer Modules
PDM 1/4/7
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