Equalization Filter (Digital Demod)
The applies the VSA's equalization filter to the measurement.
uses the measured signal to determine the coefficients of the .
When equalization is reset (see About Adaptive Equalization for conditions that reset the equalization filter), the equalization filter has a unit impulse response. The length of the filter determines the position of the unit impulse response in the filter. The impulse is located in the center of the filter for short filter lengths. As the filter length increases, the impulse moves proportionally towards the start of the filter to handle channels with large delay-spread.
If is set to , the VSA uses the results of the current measurement to update the filter coefficients for the next measurement. The VSA chooses coefficients that produce a modulation quality metric that is less impacted by the presence of linear distortion.
If is set to , the VSA does not update the filter coefficients. Instead, the VSA uses the last updated coefficients before selecting .
Select or at any time to continue or stop updating filter coefficients.
Note that the VSA does not redefine the equalization filter to have a unit impulse response when is selected or when the is turned off and then on; instead, the VSA will use the last updated filter coefficients.
Select Reset Equalizer at any time to redefine the equalization filter to have a unit impulse response.
Equalization is applied to time-domain data. To see where equalization is applied, see the Digital Demodulation Block Diagram. In this block diagram, equalization is applied in the time-domain corrections block.
Selecting a Frequency Span
For best results, make sure to select a frequency span that contains all energy of your signal. If significant energy from your signal falls outside of the displayed frequency span, equalization will not work on your signal.
Equalization Parameters
Define the length of the equalization filter (in symbols) and set the convergence (convergence determines the size of the steps used to reshape the ). For additional details about these parameters, see online help for convergence and filter length.
Viewing Impulse Response or Frequency Response
View the impulse response or the frequency response of the equalized channel by clicking , and selecting Eq Impulse Response or Ch Frequency Response.
The VSA applies the to the measurement when the Equalization Filter check box is selected. When the check box is cleared, the filter still exists and may be viewed, but is not used. The filter may be turned on and off without resetting the filter coefficients.
Equalization With Pulse and Constellation Sync Search (Digital Demodulation)
Use equalization with Pulse Search and Constellation Sync Search. Note that the adaptive equalizer does not update the filter coefficients when a "PULSE NOT FOUND" condition exists. In other words, if is on and the measurement results in a "PULSE NOT FOUND" message, the results of that measurement will not affect the equalization filter coefficients. The same is true if is on and the measurement results in a "SYNC NOT FOUND" message.
Equalization and Measurement Speed
The following parameters affect measurement speed when using adaptive equalization:
- Result Length
- Filter Length (for the equalization filter)
- Points / Symbol
See Also
