Actually, LMR-200 is good cable but not at all the best for microwave use. LMR-400 or LMR-600 would be better choices from the same vendor. RG58 is fine for VHF radios or CBs but let's not even joke about using it for microwave antennas, if any vendor is selling it for them, that's a cruel joke.
http://www.timesmicrowave.com/cgi-bin/calculate.pl
An online calculator that will tell you how much loss there is for each LMR product, per feet of run.
Fifteen feet is argubaly tolerable with a gain antenna, although using a USB cable with remote radio would make a big difference in the signal.
Lue, an am/fm radio as in "car stereo" has nothing to do with all this. Install it where convenient, they aren't very picky about antennas (even a coat hangar will often work well) and they're totally separate from computer communications systems.