Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 211)

Wave Expert
WE-OM-E Rev A
209
frequency is halfway between two discrete bin frequencies. This variation of the spectrum
magnitude is called the picket fence effect (the loss is called the scallop loss).
All window functions compensate for this loss to some extent, but the best compensation is
obtained with the Flattop window.
Power Spectrum The power spectrum (V 2 ) is the square of the magnitude spectrum.
The power spectrum is displayed on the dBm scale, with 0 dBm corresponding to:
V
ref
2 = (0.316 V
peak
) 2 ,
where V
ref
is the peak value of the sinusoidal voltage, which is equivalent to 1 mW into 50 ohms.
Power Density Spectrum The power density spectrum (V 2 /Hz) is the power spectrum divided by
the equivalent noise bandwidth of the filter, in hertz. The power density spectrum is displayed on
the dBm scale, with 0 dBm corresponding to (V
ref
2 /Hz).
Sampling Frequency The time-domain records are acquired at sampling frequencies dependent
on the selected timebase. Before the FFT computation, the time-domain record may be decimated.
If the selected maximum number of points is lower than the source number of points, the effective
sampling frequency is reduced. The effective sampling frequency equals twice the Nyquist
frequency.
Scallop Loss This is loss associated with the picket fence effect.
Window Functions All available window functions belong to the sum of cosines family with one to
three non-zero cosine terms:
where: M = 3 is the maximum number of terms, a
m
are the coefficients of the terms, N is the number
of points of the decimated source waveform, and k is the time index.