Hi Andrea,
I'm not sure what would cause that.? But I think one other user reported a similar issue, and found in the "Band configuration" window of the terminal interface that his 20M center frequency had been set to 0.? So I would at least check your band configuration settings, and see if 20m looks normal for all settings, with the band edges and center frequency appropriate for 20m. (The band edges are typically set to well below and above the ham band, and that's ok - they are used for the x-axis range of the sweep functions.)
?
Others may have additional ideas...
Stan
