Nautel NX25, Operation And Maintenance Manual

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NX300 Operations and Maintenance Manual Description
Issue 3.0 2012-11-01 Page 1-3
Figure 1.1: Exciter Stage
The digital PDM component consists of nine phased PDM signals, each separated by 40 electrical
degrees. These PDM drive signals determine the transmitter output power level as well as the output
modulation level. Three of these phases, each separated by 120 electrical degrees (e.g., 1, 4 and 7), are
applied to a given RF power module. To achieve optimal harmonic cancellation, three different
phases (e.g., 2, 5 and 8) are applied to the adjacent module, and three other phases (e.g., 3, 6 and 9) are
applied to the next module.
Samples of the RF output voltage, RF output current and RF power module temperature are
monitored. If a parameter exceeds an acceptable limit, the active exciter attempts to compensate by
decreasing its output power to restore the parameter to an acceptable level.
A sample of the B+ supply voltage is monitored. A B+ compensation circuit attempts to regulate the
regulated B+ supply in order to hold the transmitter output power constant and mimimize distortion.
An inhibit PDM input is applied from the control/display PWB to inhibit the PDM drive during
certain alarm/fault conditions.
RF drive distribution
The control/interface PWB (A11A1) accepts the RF drive (+ and -) signals from the digital AM
exciter PWBs (A and B) and splits the active exciter’s RF drive signal for application to each cabinet’s
RF drive distribution PWB (A16). The RF drive distribution PWB splits the signal from the control/
interface PWB and buffers the individual outputs that are provided to the RF power stage.
Digital AM
Exciter A
+15 V dc
-15 V dc
+5 V dc
Audio/
IBOC/
DRM
Inputs
Digital AM
Exciter B
Cont
rol/Interfac
e
Audio/
IBOC
Inputs
Control/Interface
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
T
o
RF P
o
wer Modules