Tektronix TDS5054, User Manual

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Creating and Using Math Waveforms
3- 160
TDS5000 Series User Manual
Impulse Response Testing: When performing impulse response testing of a
system, place the impulse at the zero-phase reference position of the acquisition.
This produces a correct phase display. Because the Tek Exponential window has
its zero phase reference position at the 20% point, more of the impulse response
is captured. All other window functions have their phase reference position at the
50% position in the gated region.
There are several ways to adjust the position of the zero phase reference point
with respect to your input signal:
H
Adjust the spectral analyzer gate position
H
Perform fine adjustment using the front-panel trigger level control
H
Adjust the front-panel horizontal POSITION control
Using windows to filter. There are eight different spectral analyzer windows:
H
Rectangular
H
Hamming
H
Hanning
H
Kaiser-Bessel
H
Gaussian
H
Blackman-Harris
H
Flattop2
H
TekExponential
In the time domain, a window is a bell-shaped function equal in length to the
gate duration. For most windows, this function tapers to zero at both ends of the
gate region. Before computation of the spectral transformation, the window is
multiplied, sample by sample, times the input data in the gated region. The
window function affects the shape of the spectral analyzer response in the
frequency domain. The window functions affect the ability to resolve frequency
in the output spectrum and can affect the accuracy of the magnitude and phase
measurements. Figure 3--48 shows how the time domain record is processed.