EET 422 EMC & COMPLIANCE ENGINEERING Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
SUPERHETRODYNE SPECTRUM ANALYSER Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
OUTPUT VOLTAGE PROPORTIONAL to INPUT VOLTAGE ENVELOPE PEAK DETECTOR OUTPUT VOLTAGE PROPORTIONAL to INPUT VOLTAGE ENVELOPE Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
fastest measurement speed PEAK DETECTOR fastest measurement speed highest measured value Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
HIGHER FREQUENCY = HIGHER OUTPUT QUASI-PEAK DETECTOR CHARGE RATE > DISCHARGE HIGHER FREQUENCY = HIGHER OUTPUT Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
QUASI-PEAK DETECTOR measured reading is always peak detector value easier to pass EMI tests quasi – peak slower measurement speed than peak detector (2 or 3 orders of magnitude) function of repetition rate higher voltage output as the repetition rate increases Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
QUASI-PEAK DETECTOR weigh signals according to repetition rate a measure of annoyance factor most radiated and conducted limits are based on quasi-peak detection mode Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
AVERAGE DETECTOR measured reading is always peak detector value radiated measurements above 1GHz use average mode filters average the higher frequencies Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
FAST FOURIER TRANSFORM input signal continuous input signal samples frequency domain samples Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
the machine calculation complex Fourier series FFT ALGORITHM 1805 1965: an algorithm for the machine calculation of complex Fourier series James W Cooley 1926 John W Tukey 1915-2000 Carl Frederich Gauss 1777-1855 Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING HARRY NYQUIST 1889 - 1976 (FFT 1924) SAMPLING THEOREM Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING FT ANALYSER simplification and speed of transformation number of equally spaced input samples (N) a multiple of 2 (128, 256, 512, 1024..) Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING SAMPLING correct frequency Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
Hermann Ludwig Ferdinand von Helmholtz SAMPLING THEOREM BERGMANN (FFT 1858) Hermann Ludwig Ferdinand von Helmholtz 1821-1894 (FFT 1867) Harry Nyquist 1889-1976 (FFT 1924) Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
it is completely determined by ordinates at a series of points spaced SAMPLING THEOREM Claude Elwood Shannon 1916-2001 (FFT 1949) “if a function f(t) contains no frequencies> f (Hz) it is completely determined by ordinates at a series of points spaced Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
traditional bandwidth discrete functions with finite spectra transmission without significant signal attenuation over a frequency range discrete functions with finite spectra bandwidth = the highest frequency in the spectrum aliter: continuous functions finite bandwidth if all Fourier coefficient magnitudes are zero beyond some limiting frequency W Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
to reconstruct a band limited function exactly over a finite interval a finite number of samples reconstruction without error sampling rate R exceeds 2W FFT transforms N equally spaced time domain samples to N/2 equally spaced lines in the frequency (each frequency line amplitude and phase) Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING ALIASING analyser range Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
alias frequency fa = fsampling - fsignal NO aliasing sampled signal has correct frequency aliasing alias frequency fa = fsampling - fsignal aliasing n = CIM = Closest Integer Multiple of fsampling aliasing alias frequency fa = 0 Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING EXAMPLE Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING EXAMPLE Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING EXAMPLE Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING AVOIDING ALIASING SIGNAL RANGE ALIAS RANGE Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING 1 rpm 1 cycle / 60 sec Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING WINDOWING (a) (b) (c) Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING PERIODIC: FFT OK Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING PERIODIC: FFT OK Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING NON-PERIODIC Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING HANNING WINDOW Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING WINDOW FUNCTIONS Hanning Window Flat-top Window Rectangular Window Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
BETTER FREQUENCY ACCURACY than AMPLITUDE ACCURACY HANNING WINDOW BETTER FREQUENCY ACCURACY than AMPLITUDE ACCURACY Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING HANNING WINDOW WINDOW NOT GOOD Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
BETTER AMPLITUDE ACCURACY ACCURACY than FREQUENCY ACCURACY FLAT-TOP WINDOW BETTER AMPLITUDE ACCURACY ACCURACY than FREQUENCY ACCURACY Prof R T Kennedy EMC & COMPLIANCE ENGINEERING
EMC & COMPLIANCE ENGINEERING Oscilloscope Frequency Domain Spectrum Analyser Time Domain Prof R T Kennedy EMC & COMPLIANCE ENGINEERING