Do you know how I can cure this problem?
Also --- the 1.33MHz is a local Am station with a lot of power.
You could try placing a well-designed broadcast frequency trap in front of the antenna input. I'd look into designing one that could be tuned to that frequency of interest rather than a broadbanded type. http://www.dxing.com/tnotes/tnote06.pdf
Don't count on being ale to make the thing perform like something it isn't, though.