On my "old" GRE scanner I listen to three simulcast systems, with problems.
The solution is LESS antenna. I have an old UHF "rubber duck" from a handheld that has a BNC connector.
I also have a small mag mount with a mating BNC, in the North facing window .
I listen to the Cleveland system, Summit county and MARCS, with no trouble.
NOTE ; this is a fixed location !