How long a run are you contemplating? The reason I ask is that unless it is going to be 100 feet or more you probably wouldn't notice the 2-3db difference AND getting clamp connectors for LMR-400 can be expensive unless you already own the correct crimp tool to go with crimp connectors. You'd get far more bang for your buck using RG-58 or RG-8x and a feedline-powered preamplifier up on them mast...or just slap some cheap quad-shield RG-6 from Home Depot in there and be done with it since the scanner doesn't care much about the match and a ground plane antenna won't either, especially if you bend the radials down to about 60 degrees instead of 45.