Intermodulation cause in BTS antenna

just some initial random thoughts.....
identifying the sources of the intermod, ie, the other transmitter signals that are involved in the mixing and applying very good filtering.

I would hope that you are using isolators on the outputs of your own transmitters to stop them retransmitting other intermod products ? :)

cheers
Dave

Also beware of dirty or poor connections anywhere in your system
(Doubly so in damp or dirty environments)
I've seen bad connections "tuning" stuff you wouldnt normally see.

jack