National Instruments Toolkit

NI Spectral Measurements Toolkit User Guide 32 ni.com

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.

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()

∑

ENBW

------------------ Window size

FFT size

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×=