It can be awkward to synchronise the starting/stopping of collecting data with the starting/stopping of antenna rotation. There is a facility to get PolarPlot to detect the presence or absence of a signal to signify start and stop of collection.
In the top left of the controls area of the screen there are two check boxes, one for Auto Start and one for Auto Stop. You can enable and disable these functions by clicking in the checkbox.
Both Auto Start and Auto Stop have a trigger level that is customisable from the PolarPlot Settings screen which you get to by double clicking on the plot area of the screen.
Auto Start has two parameters - an input trigger level below which any signal received is ignored for signalling start of collection, and a delay between the trigger level being reached and the start of collection. You can use these parameters to cater for background noise if conditions are bad and transmitter warm-up delays, if any, exist.
Auto Stop also has two parameters - an input trigger level below which any signal received is treated as potentially signalling end of collection, and the number of consecutive readings below the trigger level that must be received before collection is halted. This enables you to continue collecting readings even if a deep null is encountered in the radiated pattern. If Auto Stop is used then these 'surplus' readings are automatically trimmed from the back.