Plot Scaling

Plots can be scaled by means of Plot Scaling dialog (Fig. 17). The dialog enables you to control:

  • The span of the axes for the rectangular plot types.

  • Radii of the circular plot types.

Fig. 17.  Plot Scaling dialog box.

Plot Scaling dialog for the active display window can be invoked by any of the following alternatives:

  • Click the button on the display window toolbar.

  • Click the Scale|Set Scale menu item.

  • Double-click the top-level Scale menu item.

  • Use the Ctrl+Y shortcut.

The dialog box contains several panels, of which only those pertinent to the particular display type are accessible.

Rectangular Plots

Xmin, Xmax

User-defined lower and upper bounds of the x-axis. The x-axis is labeled Points and represents the sequential number of a measurement point.

Points

Points is a non-editable information field showing the number of currently selected trace points (points per sweep). Points per sweep can be defined by Homer|Points per Sweep, the  Pts  toolbar button, or the Ctrl+N shortcut.

Automatic

If the Automatic checkbox is checked, the span of x-axis is given by points per sweep (Np). The lower bound is zero, the upper bound is equal to (Np – 1). The Xmin, Xmax edits are disabled and their settings ignored. If the box is unchecked, the span of x-axis is given by the Xmin, Xmax values.

The x-axis grid spacing is always automatic.

Ymin, Ymax

User-defined lower and upper bounds of the y-axis. The values will be accepted after you click the  OK  button. The values will be ignored if you click the  Auto ,  Default  or  Cancel  button.

Integral

When the Integral checkbox is checked, the y-axis span will be an integral multiple of the axis grid interval. The span encompasses the complete interval Ymin to Ymax. The plot will have a neat appearance but there may be unused portions up to one grid interval at the bottom and top.

When the Integral box is unchecked, the plot y-axis bounds will be equal to Ymin, Ymax, or as returned by the autoscaling procedure. The bounds will not be “neat” numbers but the plot span will be used in a more efficient way.

The y-axis grid spacing is always automatic.

Circular Plots

Polar Plot

With Polar plot, only the Polar radius (POLAR R) field is enabled. Here you can enter the desired radius of the polar plot. The choice will be accepted after clicking the  OK  button.

Smith Charts, Oven Plot

For these types of displays, only the Smith radius (SMITH R) radio group is enabled. Here you can select from available polar radii one which best accommodates the measured data. Confirm by the  OK  button.

Buttons

OK

Accept the settings and close the dialog.

Auto

Autoscaling of the y-axis based on the latest measured data.

Rectangular plots: After clicking the  Auto  button, the minimum and maximum y-coordinates of all simultaneously displayed traces are computed. Using these values, the y-axis bounds of the plot are automatically set to accommodate all traces. The Integral checkbox status is also considered. The values in the Ymin, Ymax fields are modified accordingly.

Circular plots: A similar method is used to compute the polar radius.

The function will only be activated when measured data are available. The function can also be invoked by the Scale|Autosacale menu item, Ctrl+A shortcut or sbAutScale display window button.

Back

Clicking the  Back  button returns scale settings to the most recent manually entered values. The button is useful for reverting autoscale settings. The button does not work with Smith chart and Oven plot types.

Default

Clicking the  Default  button sets the y-axis span or polar radius to a fixed default value, usually covering the entire possible or practical span of the displayed quantity. Unlike  Auto , the function can be activated anytime and does not affect the fields of the dialog box.

The function can also be invoked by the Scale|Default menu item, Ctrl+D shortcut or the  Dflt  display window toolbar button.

Cancel

Ignore new settings and close the dialog.