Power & Frequency Estimate VI

Power Spectrum is the power spectrum of a time domain signal. Power Spectrum is the output of the Auto Power Spectrum VI.

peak frequency is the frequency, usually in hertz, of the frequency peak around which you want to estimate the frequency and power. The default is –1. If you do not wire this parameter, the VI automatically searches for the maximum peak in the power spectrum array and estimates the frequency and power around it.

window constants specifies the property constants of a window. If you apply a window to a time-domain signal to avoid spectral leakage when you compute the power spectrum of the signal, you can use window constants to compensate for the effect of the window you apply. The default values are set to those of the rectangular window (no window). window constants is usually the output of the Scaled Time Domain Window VI.

	eq noise BW is the equivalent noise bandwidth (ENBW) of the window that was used. The default is 1.0. You can use this value to divide a sum of individual power spectra of the power spectrum or to compute the power in a given frequency span.
	coherent gain is the inverse of the scaling factor applied to the window. The default is 1.0.

df is the frequency interval of the power spectrum. The default is 1.0.

span is the number of frequency lines (bins) around the peak to be included in the peak frequency and power estimation. The default is 7, which means that the power in three frequency lines before the peak frequency line, the peak frequency line itself, and three frequency lines after the peak are included in the estimation. This is adequate for most windows.

est frequency peak is the estimated frequency of the peak in the input Power Spectrum. est frequency peak is computed as

for j = i – span/2, …i + span/2,

where i = peak index, Power Spectrum (j) = power in bin j, and df = frequency bin width.

est power peak is the estimated power of the peak in the input Power Spectrum. est power peak is computed as

for j = i – span/2, …i + span/2,

where i = peak index, Power Spectrum (j) = power in bin j, and ENBW = equivalent noise bandwidth of the window.

Power & Frequency Estimate Details

With the Power & Frequency Estimate VI, you can achieve good frequency estimates for measured frequencies that lie between frequency lines on the spectrum. The Power & Frequency Estimate VI also makes corrections for the window function you use.

Example

Refer to the Power & Frequency Estimator VI in the labview\examples\Signal Processing\Spectral Analysis directory for an example of using the Power & Frequency Estimate VI.

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