have you guys ever heard of something called the 3rd harmonic?
http://www.physicsclassroom.com/mmedia/waves/harm3.cfm

Let me explain...
A while ago my next door neighbour was experiencing some interference with his sky tv and while I was on holiday the interference stopped, then upon my return home, the interference started again, next minute I receive a knock at my door from the UK body that allocates the frequencies trying to figure out what I was using that was interfering with my next door neighbour's sky tv....

it turned out that my then wireless broadband signal (using LOS dish) were bouncing of some walls and also bouncing off his sky mini dish and causing interference at another frequency, i think around a multiple of x3, hence called the 3rd harmonic... basically if you listen for a signal on other frequencies that can be divided/multiplied by x2/x3/etc (the third harmonic being the stronger), then you could identify other RF nearby...

...in my case tests showed that the 3rd harmonic interference was being picked up at around 300 meters away very strongly.

the outcome of this was that whoever in the uk allocated the air frequencies originally did not think of the 3rd harmonic and I was not asked to stop using the service.