IF Dither

You can enable IF dithering for additional image and spur protection:

IF Dither Auto - when checked, the 89600 VSA software automatically turns on IF Frequency dither based on the hardware you are using and the resolution bandwidth (RBW Resolution Band Width (RBW or ResBW): specifies the minimum frequency bandwith that two separate frequency spectra can be resolved and viewed seperately. For FFT (digital) based VSA's the process is equivalent to passing a time-domain signal through a bank of bandpass filters, whose center frequencies correspond to the frequencies of the FFT bins. For a traditional swept-tuned (non-digital) spectrum analyzer, the resolution bandwidth is the bandwidth of the IF filter which determines the selectivity.). Auto IF Frequency Dither turns dithering on for lower RBWs and turns it off for higher RBWs. When on, the IF Dither on/off radio buttons are automatically selected based upon the resolution bandwidth.
IF Dither On/Off - when selected, turns on/off IF Frequency Dithering, which provides further protection from internally generated spurs and images.