If you are referring to Times-Microwave brand LMR cable there are many different models, everything from LMR-100 up to LMR-900, and they vary quite a bit.
You need to be more specific.
As was suggested, how did you test it? What type of test did you do, and what type of test equipment (again, be specific).
There can be a lot of reasons for a setup like this to not work well. Everything from cable issues to high RF levels near the antenna. Providing some background info would give us enough information to assist you in your troubleshooting.