Tektronix SPECMON3 Manual page 327

GP Digital Modulation
Selecting the Mode
When enabled, the Equalizer is in either Train mode or Hold mode. When the equalizer is in Train mode, it
will update internal filter parameters whenever you adjust the Convergence, Taps/Symbol, Taps, or Length
values. When it is in Hold mode, the Equalizer uses the parameter values (both internal and the values
accessible on the Equalizer tab) in effect when it was placed into Hold mode.
NOTE. The Equalizer does not need to be retrained if the modulation type is changed. You can train the
Equalizer by using a simpler modulation type (such as QPSK), place the Equalizer into Hold mode and
can then measure more complex modulation types such as QAM.
Training the Equalizer
To obtain the desired results using the Equalizer, you must first train the Equalizer. This is an iterative
process where you adjust some filter parameters (and the analyzer adjusts internal parameters) to achieve
the lowest error possible on the acquired signal.
To configure the Equalizer:
1. Press the Displays button or select Setup > Displays.
2. In the Select Displays window, select GP Digital Modulation from Folders.
3. Add Signal Quality to the Selected Displays and select OK.
4. With the Signal Quality display selected, select Setup > Settings.
5. Select the Modulation Params tab set the parameters as necessary for the signal.
6. Select the Equalizer tab.
7. Set the Convergence value to 0.0005.
8. Set Taps/Symbol to 2.
9. Click the Reset Equalization button to reset the equalizer.
10. Set the Mode to Train.
11. Click Enable Equalization so it is checked.
12. On the Signal Quality display, examine the value for EVM.
13. Change the Convergence, Taps/Symbol, and Taps values iteratively to achieve a minimum EVM value.
NOTE. Changing the Taps/symbol or Taps values resets the equalizer.
Using the Equalizer
To use the equalizer:
1. Select and configure a GP Digital Modulation display.
2. Select Setup > Settings.
SPECMON3 & SPECMON6 Printable Help
Equalizer Tab
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