1. EET 422 EMC & COMPLIANCE ENGINEERING
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

2. EMC & COMPLIANCE ENGINEERING
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

3. SUPERHETRODYNE SPECTRUM ANALYSER
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

4. OUTPUT VOLTAGE PROPORTIONAL to INPUT VOLTAGE ENVELOPE
PEAK DETECTOR
OUTPUT VOLTAGE PROPORTIONAL to
INPUT VOLTAGE ENVELOPE
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

5. fastest measurement speed
PEAK DETECTOR
fastest measurement speed
highest measured value
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

6. HIGHER FREQUENCY = HIGHER OUTPUT
QUASI-PEAK DETECTOR
CHARGE RATE >
DISCHARGE
HIGHER FREQUENCY = HIGHER OUTPUT
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

7. 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

8. 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

9. 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

10. FAST FOURIER TRANSFORM
input signal continuous
input signal samples
frequency domain samples
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

11. 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
Carl Frederich Gauss
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

12. EMC & COMPLIANCE ENGINEERING
HARRY NYQUIST
(FFT 1924) SAMPLING THEOREM
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

13. EMC & COMPLIANCE ENGINEERING
FT ANALYSER
simplification and speed of transformation
number of equally spaced input samples (N)
a multiple of 2 (128, 256, 512, )
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

14. EMC & COMPLIANCE ENGINEERING
SAMPLING
correct frequency
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

15. Hermann Ludwig Ferdinand von Helmholtz
SAMPLING THEOREM
BERGMANN
(FFT 1858)
Hermann Ludwig Ferdinand von Helmholtz
(FFT 1867)
Harry Nyquist (FFT 1924)
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

16. it is completely determined by ordinates at a series of points spaced
SAMPLING THEOREM
Claude Elwood Shannon
(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

17. 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

18. 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

19. EMC & COMPLIANCE ENGINEERING
ALIASING
analyser range
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

20. 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

21. EMC & COMPLIANCE ENGINEERING
EXAMPLE
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

22. EMC & COMPLIANCE ENGINEERING
EXAMPLE
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

23. EMC & COMPLIANCE ENGINEERING
EXAMPLE
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

24. EMC & COMPLIANCE ENGINEERING
AVOIDING ALIASING
SIGNAL RANGE
ALIAS RANGE
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

25. EMC & COMPLIANCE ENGINEERING
1 rpm
1 cycle / 60 sec
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

26. EMC & COMPLIANCE ENGINEERING
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

27. EMC & COMPLIANCE ENGINEERING
WINDOWING
(a)
(b)
(c)
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

28. EMC & COMPLIANCE ENGINEERING
PERIODIC: FFT OK
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

29. EMC & COMPLIANCE ENGINEERING
PERIODIC: FFT OK
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

30. EMC & COMPLIANCE ENGINEERING
NON-PERIODIC
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

31. EMC & COMPLIANCE ENGINEERING
HANNING WINDOW 
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

32. EMC & COMPLIANCE ENGINEERING
WINDOW FUNCTIONS
Hanning Window
Flat-top Window
Rectangular Window
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

33. BETTER FREQUENCY ACCURACY than AMPLITUDE ACCURACY
HANNING WINDOW
BETTER FREQUENCY ACCURACY
than
AMPLITUDE ACCURACY
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

34. EMC & COMPLIANCE ENGINEERING
HANNING WINDOW
WINDOW NOT GOOD
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

35. BETTER AMPLITUDE ACCURACY ACCURACY than FREQUENCY ACCURACY
FLAT-TOP WINDOW
BETTER AMPLITUDE ACCURACY ACCURACY
than
FREQUENCY ACCURACY
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING

36. EMC & COMPLIANCE ENGINEERING
Oscilloscope
Frequency Domain
Spectrum Analyser
Time Domain
Prof R T Kennedy
EMC & COMPLIANCE ENGINEERING