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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:
Adjust the spectral analyzer gate position
Perform fine adjustment using the front-panel trigger level control
Adjust the front-panel horizontal POSITION control
Using Spectral Analyzer Windows
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. The preceding figure
shows how the time domain record is
processed.
Accurate magnitude measurements require that the input source waveform be stationary within the
gated region. This means that waveform parameters such as frequency and amplitude should not
change significantly as a function of time within the gate region that is input to the spectral
analyzer. Also, the gate width must be greater than or equal to the period of the start frequency of
the span of the spectral analyzer. That is, there must be at least one cycle of the harmonic being
measured within the gated region.
There are eight different spectral analyzer windows:
Rectangular Hamming
Hanning Kaiser-Bessel
Gaussian Blackman-
Harris
Flattop2
TekExponential
Summary of Contents for TDS5000B Series
Page 36: ...36 AFTDS Differential Signal Adapter...
Page 280: ...280 Blackman Harris window...
