Oscilloscope Reference Spectral math phase controls
Group delay measures how well a system p asses a signal in terms of phase distortion. Group delay is the
derivative of the phase with respect to frequency.
This feature is not useful for analysis of harmonic content of signals where the phase response is not
continuous.
Impulse response testing
When perfor
ming 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
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.
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The w indow functions affect the ability to resolve frequency in the output spectrum and can affect the
accuracy of the magnitude and phase measurements. The previous figureshowshowthetimedomain
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 ga t e
768 DSA/DPO70000D, MSO/DPO/DSA70000C, DPO7000C, and MSO/DPO5000 Series
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