LeCroy SDA, Руководство оператора

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Window Type Applications and Limitations
Rectangular These are normally used when the signal is transient (completely contained in
the time-domain window) or known to have a fundamental frequency component
that is an integer multiple of the fundamental frequency of the window. Signals
other than these types will show varying amounts of spectral leakage and
scallop loss, which can be corrected by selecting another type of window.
Hanning (Von
Hann)
These reduce leakage and improve amplitude accuracy. However, frequency
resolution is also reduced.
Hamming These reduce leakage and improve amplitude accuracy. However, frequency
resolution is also reduced.
Flat Top This window provides excellent amplitude accuracy with moderate reduction of
leakage, but with reduced frequency resolution.
Blackman–
Harris
It reduces the leakage to a minimum, but with reduced frequency resolution.
Improving Dynamic Range
Enhanced resolution uses a low-pass filtering technique that can potentially provide for three
additional bits (18 dB) if the signal noise is uniformly distributed (white). Low-pass filtering should
be considered when high frequency components are irrelevant. A distinct advantage of this
technique is that it works for both repetitive and transient signals. The SNR increase is
conditioned by the cut-off frequency of the ERES low-pass filter and the noise shape (frequency
distribution).
LeCroy digital oscilloscopes employ FIR digital filters so that a constant phase shift is maintained.
The phase information is therefore not distorted by the filtering action.
Record Length
Because of its versatility, FFT analysis has become a popular analysis tool. However, some care
must be taken with it. In most instances, incorrect positioning of the signal within the display grid
will significantly alter the spectrum. Effects such as leakage and aliasing that distort the spectrum
must be understood if meaningful conclusions are to be arrived at when using FFT.
An effective way to reduce these effects is to maximize the acquisition record length. Record
length directly conditions the effective sampling rate of the scope and therefore determines the
frequency resolution and span at which spectral analysis can be carried out.
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