We use two different IF frequencies when software image/spur reject is active and span is 200 kHz or less: 2.9 MHz and 10.7 MHz. The image frequency is [RF frequency] + 2 * [IF frequency]
Internal measurements will be made with the 2.9 MHz IF, followed by the 10.7 MHz IF. The lower reading for each frequency bin is displayed.
If you disable spur reject, only the 10.7 MHz IF will be used.
The BB60 or SM200 is a better choice for noise measurements, since the image is rejected in hardware, and software spur reject is off by default.
