NI Spectral Measurements Toolkit User Guide 32 ni.com

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 V2rms. 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, fl and fh 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 thecenter 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 inputvalue.
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
Xf()
fl
fh
ENBW
------------------ Window size
FFT size
------------------------------
×=