What gauge of speaker wire to use

Just a suggestion, but I would discuss the issue with the radio station. Surely they have an engineer on staff that could help.

I think though, that some sort of isolator would be a better option than different awg wire. You would need to find out what frequency they are broadcasting at and get isolators that kill that range. Insulated wire might help, but probably not completely.

Another place that may offer some help is Guitar Center. They sell a lot more than just guitars. http://www.guitarcenter.com/