Dimwitted channel planning, wrong equipment & settings or what.
http://paradigma.pt/ja/slog/index.ph...s-overlap.html
Bigger -
http://paradigma.pt/ja/slog/wp-conte...hannel-map.JPG
For a start, the UK/ETSI allocation is 1-13, not 1-11, but there are too many only implementing / set to 1-11 to gain much from the 1-13 allocation.
A spacing of 5 is required for no overlap, giving the ever popular 1-6-11 layout.
A spacing of 4 has minimal overlap, giving the optimum 1-5-9-13 layout for the 13 channel allocation, though 9 tends to be the centre of microwave oven interference.
A spacing of 3 (some overlap) gives the compromise 1-4-7-11 4 channel lineup.
At a spacing of 2, one sideband fully overlaps another, so those using channel 3 in that setup are not doing anyone any favours, as they will be going badly over CH1 and moderately over CH6.
If not close to a CH11 user, then using CH13 may be better.