Step size in time and the amplitude of the carrier during the duration of the pulse are user-defined. Note that AM step is an intra-pulse modulation and not amplitude modulation from pulse to pulse. The amplitude offset is a relative parameter and must be within the power limits of the signal generator's baseband generator. The maximum amplitude is used as the reference; all lower power levels are relative to the maximum amplitude step.
For the trapezoidal and raised-cosine built-in pulse types the step size should sum to equal the pulse Width (100%-100%). For custom profile and custom I/Q pulse types the step size should sum to equal the time duration from the first point of data through to the last point of data. Selecting the AM Step Modulation Type displays an AM step table shown in the figure below. If the step size does not equal the pulse width, the AM steps will be padded (if not enough steps), or truncated (if too many steps). Refer to the padded and truncated diagram for more information.
When using the AM Step modulation format the ALC should be turned off, or the ALC Hold feature should be used. This prevents the ALC from trying to level the AM step within the pulse.
To create the AM step table:
Select AM Step from the Modulation Type drop-down list box.
Place the mouse pointer in the AM step table and click the right mouse button.
Click 
New Items
in the menu.
Enter the number of
index items
desired using the dialog box.
Enter the step size and amplitude for each index item.
In the following diagram the frequency offset and time duration relationship for the table entries in the above figure are shown. Note that modulation is applied only during the pulse Width (100%-100%) time interval and not during rise and fall times. In the diagram below the last half of the –15 dB step, and the entire 0 dB step will not modulate the pulse because they occur after the pulse width of 8 us. See the section on padding and truncating.
