Nautel NX300, Operation And Maintenance Manual

Page: 118 / 162

NX300 Operations and Maintenance Manual Operating the transmitter
Page 2-100 Issue 3.0 2012-11-01
AM-AM Correction
The
AM-AM Correction
page (see Figure 2.76 ) allows you to load or capture a set of AM-AM
correction curves. You can
Load
or
Delete
curves in this list; you can also capture a curve. When
you select
Capture
, the AM-AM Correction window is displayed. Press
Done
to capture the curve,
type a name for the curve, then press
Save
(or
Cancel
).
Value changes are not typically required. Up to three curves can be saved in memory.
AM-AM curves correct for a type of non-linearity where a change in input amplitude does not cause
a linearly proportional change in output amplitude. By applying a test signal and monitoring the
output of the transmitter, the exciter will generate a table of values describing the required gain versus
input signal level in an attempt to find the inverse curve to the AM-AM non-linearity, and provide a
more linear amplifier. Applying the proper AM-AM correction will result in lower audio distortion
and better spectral performace in digital modes of operation.
Figure 2.76: Precorrection AM-AM
CAUTION:
Making changes to the AM-AM Correction curves automatically places the
transmitter in analog AM mode, with full-scale sine-wave modulation. To avoid
undesirable output or possible antenna damage, it is highly recommended that
you perform these calibrations while operating the transmitter into a test load.