Table D 3: Values Of Wcoeff And M For Fft Windowing Functions - Tektronix 11801C User Manual

Appendix D: Algorithms
D 22

Table D 3: Values of wcoeff and m for FFT Windowing Functions

FFT Window wcoeff(0)
Blackman 0.42
Blackman Harris 0.35875
Hamming 0.54
Hanning 10.5
Rectangular 1.0
Triangular 0.5
3. For the nth harmonic magnitude, compute the harmonic frequency and
apply the previous algorithm.
In Peak Search Mode
nitude correction to the spectral component which is the nth peak of the FFT
magnitude waveform.
Total Harmonic Distortion (THD)
See also Frequency Domain Measurements on page D 16.
1. Determine the fundamental frequency.
2. Find the magnitude of the spectral peak and of adjacent values:
S( * 1) , S( ) , S( ) 1) in the FFT magnitude waveform,
(S( * 1))
A + S( ) )
1
S( * 1) ) S( ) ) S( ) 1)
3. Find the first n harmonic components and determine the three highest
waveform points in the FFT magnitude waveform, S( * 1) , S( ) ,
S( ) 1) compute:
S( * 1) ) (S( ) 1)
A + S( ) )
n
S( * 1) ) S( ) ) S( ) 1)
n + 2, . . . , 10
4. Compute Total Harmonic Distortion
A ) A
2
2 3
THD +
wcoeff(1)
-0.5
-0.48829
-0.46
-0.5
0
0
apply the FFT interpolation algorithm and mag
) (S( ) 1))
2 2
) .... ) A
2 2
10
A
1
wcoeff(2) wcoeff(3)
0.08 0
0.14128 -0.01168
0 0
0 0
0 0
0 0
Appendices
m
2
3
1
1
0
1