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NX5 OPERATION & MAINTENANCE MANUAL
DESCRIPTION
PAGE 3.1.4
VERSION 0.1 2015-08-01
Figure 3.1.1: Exciter Stage
The digital PDM component consists of six phased PDM signals, each separated by 60 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, 3 and 5), are
applied to a given RF power module. To achieve optimal harmonic cancellation, three different phases
(e.g., 2, 4 and 6) are applied to the adjacent module.
Samples of the RF output voltage, RF output current, SCR rectifier temperature 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 adjusts the PDM duty cycle
to compensate for variations in the B+ supply in order to maintain constant transmitter output power
and mimimize hum.
A PDM inhibit (A or B) input is applied from the control/interface PWB to inhibit the PDM drive for a
specific exciter during certain alarm/fault conditions.
RF Drive Distribution
The control/interface PWB (A4) accepts the RF drive (+ and -) signals from the digital AM exciter PWBs
(A and B) and buffers the individual RF drive 1 and 2 outputs that are provided to the rack interface
PWB.
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
Modulation
Inputs
C
on
trol/
Inter
face
RF Drive (A)
RF Drive (B)
PDM (A)
PDM (B)
RF Drive 1
RF Drive 2
PDM 2/4/6
To
RF P
ower
Mo
dules
PDM 1/3/5
Summary of Contents for NX5 AM
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