Nautel NX50, Operation And Maintenance Manual, Page: 11 / 166

NX50 Operations and Maintenance Manual Description
Issue 3.3 2016-02-08 Page 1-3
Exciter Stage
See electrical schematic
SD-2
and Figure 1.1 . The exciter stage consists of digital AM exciter PWBs A
(A11A2) and B (A11A3), RF drive distribution PWB (A16), and PDM distribution PWB (A17). 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 or IBOC inputs from an
integrated DRM exciter or Exgine card and generate fully digital RF drive carrier frequency sources
and interphase PDM drive signals for the power amplifiers and modulators in the RF power modules.
Audio input can be applied as as analog (balanced or AES-EBU) or digital (I/Q in AES/EBU or
CMOS format). All audio inputs are digitized, as necessary, 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.
Figure 1.1: Exciter Stage
Digital AM
Exciter A
+15 V dc
-15 V dc
+5 V dc
Audio/
IBOC/
DRM
Inputs
Digital AM
Exciter B
C
ontrol/
Interface
Audio/
IBOC
Inputs
Cont
rol/Interfac
e
RF Drive (A)
RF Drive (B)
PDM (A) 1-9
PDM (B) 1-9
RF Drive 1
RF Drive 2
PDM 1-9
RF Drive
Distribution
PDM
Distribution
To
RF Power Modules