Radiation from another radar operating at the same wavelength can be received if propagation paths are suitable. On PPI interference appears as a pattern of dots, often in spirals, in a sector roughly in the direction of the other radar. The pattern is seen over a range of bearings since propagation is generally by forward scatter the aerials need not be pointing exactly at one another. Where interference is troublesome it can sometimes be tuned out by a slight change in operating wavelength of either radar.