NI Spectral Measurements Toolkit User Guide
32
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Power in Band
The SMT Power in Band VI, located on the
SMT Measurements
palette
measures the total power within some frequency range or band.
X
is the
input power spectrum in V
2
rms
. Perform this measurement before
performing unit conversion. Enter a center frequency and bandwidth in Hz,
from which you can derive the low and high bounds,
f
l
and
f
h
respectively,
of the frequency band. The SMT Power in Band VI computes the total
power using the following formula:
The SMT Power in Band VI calculates the powers at each of the
frequencies lying in the band. The VI then applies a correction for spectral
leakage from windowing and for any zero-padding. The SMT Power in
Band VI can calculate power in band in units such as W, dBW, and dBm,
using an impedance that you supply.
Adjacent Channel Power (ACP)
The SMT Adjacent Channel Power VI, located on the
SMT
Measurements
palette, measures the way a center channel and its two
adjacent channels distribute power. Use this VI before using the SMT
Spectrum Unit Conversion VI.
Channel
refers to a particular frequency
band of interest. The parameters
center frequency
,
bandwidth
, and
spacing
describe the three channels. The
center frequency
parameter
refers to the center frequency of the middle channel. The
bandwidth
parameter defines the width of each channel. The
spacing
parameter
defines the distance between the center of the middle channel and the
center of the upper and lower channels. These three parameters fully define
three individual frequency bands. You can specify various output units by
supplying an impedance input value.
Note
You can use the SMT Adjacent Channel Power (Advanced) VI to measure power for
an arbitrary number of adjacent channels at user-specified bandwidths and offsets from the
center frequency.
Power in Band
X f
( )
f
l
f
h
∑
ENBW
------------------
Window size
FFT size
------------------------------
×
=
