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Rescaling the plot


Click on the 'Rescale' button.  For a circular plot the program now spreads the readings actually taken over a full 360 (or 180) degrees and joins up the dots with a series of lines.  The half-power points are found and two lines drawn, with the angle between the lines shown, together with an indication of gain in dBi.  For a rectangular plot the readings are 'stretched' to fill the full width of the area.

Depending on how you collected the readings, manual or automatic, you may find that there are surplus readings at the start and end that should not be included on the plot.  These can be removed by using the 'Readings Trimmed'.  Type the number of readings you wish to exclude in 'Front' or 'Back' boxes as appropriate.

For circular plots, the program attempts to automatically rotate the plot to show the main lobe pointing north on the plot.  If the main lobe is not pointing in the direction you want you can rotate the plot by typing the number of degrees required in the 'Degrees Rotated' box. 

When showing a log scale you can change the 'look' of the plot whilst retaining the accuracy of the position of the plotted points on the screen by varying the scaling factor used.  Use 'Rescale Plot' slider to do this.  Low values (slider towards the top) will compress the centre and expand the outer rings; high values (slider towards the bottom) will do the reverse.

If the main lobe appears to be flattened, then it is likely that the receiver AGC has operated during the plot. This can be corrected with a re-run of the plot with a lower setting for RF gain. If reducing RF gain and increasing AF gain does not resolve the problem, then look into possible input level capping in the sound card.