RfsaFftWindowType Enumeration

No window is applied.

The Hanning window is useful for analyzing transients longer than the time duration of the window, and also for general-purpose applications. A Hanning window is applied to the waveform using the following equation:

y[i] = 0.5 * x[i] * [1 – cos(w)]

where

w = (2π)i / n

n is the waveform size.

A Hamming window is applied to the waveform using the following equation:

y[i] = x[i] [0.54 - 0.46 cos(w)]

where

w = (2π)i / n

n is the waveform size

A Blackman-Harris window is applied to the waveform using the following equation:

y[i] = x[i] × [0.42323 – 0.49755 cos(w) + 0.07922 cos(2w)]

where

w = (2)i / n

n is the waveform size

An Exact Blackman window is applied to the waveform using the following equation:

y[i] = x[i] * [a<format type="subscript">0</format> – a<format type="subscript">1</format> cos(w) + a<format type="subscript">2</format> cos(2w)]

where

w = (2π) i / n

n is the waveform size

a<format type="subscript">0</format> = 0.42659

a<format type="subscript">1</format> = 0.49656

a<format type="subscript">2</format> = 0.076848667

A Blackman window is useful for analyzing transient signals, and provides similar windowing to Hanning and Hamming windows but adds one additional cosine term to reduce ripple. A Blackman window is applied to the waveform using the following equation:

y[i] = x[i] × [0.42 – 0.50 cos(w) + 0.08 cos(2w)]

where

w = (2 π)i / n

n is the waveform size

The fifth-order Flat Top window has the best amplitude accuracy of all the window methods. The increased amplitude accuracy (±0.02 dB for signals exactly between integral cycles) is at the expense of frequency selectivity. The Flat Top window is most useful in accurately measuring the amplitude of single frequency components with little nearby spectral energy in the signal. A fifth-order Flat Top window is applied to the waveform using the following equation:

y[i] = x[i] × [a0 – a1 cos(w) + a2 cos(2w) – a3 cos(3w) + a4 cos(4w)]

where

w = (2π)i/n

n is the waveform size

a0 = 0.215578948

a1 = 0.41663158

a2 = 0.277263158

a3 = 0.083578947

a4 = 0.006947368

A 4 term Blackman-Harris window is a general purpose window; it has side-lobe rejection in the upper 90 dB, with moderately wide side-lobe. A 4-term Blackman Harris window is applied to the waveform using the following equation:

y[i] = x[i] * [0.422323 - 0.49755 cos(w) + 0.07922 cos(2w)]

where w = (2 π)i / n

n is the waveform size<para>

A 7 term Blackman-Harris window has the highest dynamic range; it is ideal for signal-to-noise ratio applications. A 7-term Blackman Harris window is applied to the waveform using the following equation:

y[i] = x[i] * [a<format type="subscript">0</format> - a<format type="subscript">1</format> cos(w) + a<format type="subscript">2</format> cos(2w) - a<format type="subscript">3</format> cos(3w) + a<format type="subscript">4</format> cos(4w) - a<format type="subscript">5</format> cos(5w) + a<format type="subscript">6</format> cos(6w)]

where

w = (2 pi)i/n

n is the waveform size

a<format type="subscript">0</format> = 0.27105140069342

a<format type="subscript">1</format> = 0.43329793923448

a<format type="subscript">2</format> = 0.21812299954311

a<format type="subscript">3</format> = 0.06592544638803

a<format type="subscript">4</format> = 0.01081174209837

a<format type="subscript">5</format> = 0.00077658482522

a<format type="subscript">6</format> = 0.00001388721735

The Low Side Lobe window reduces the size of the main lobe.

A Gaussian window is applied to the waveform using the following equation:

y[i] = x[i] * e<format type="superscript">((-0.5(i - (N -1 ) / 0.5)/(σ(N - 1) / 0.5))</format>

where<para>N is the length of the window

σ ≤ 0.5

A Kaiser-Bessel window is applied to the waveform using the following equation:

y[i] = x[i] * I0 * (n * a(1 - (2i / (N-1)-1)^2)^0.5)/(I0 * n * a)

where i ≥ 0 and i ≤ N-1

N is the length of the window

a determines the shape of the window

I0 is the zeroth order Modified Bessel function of the first kind