If you go with a puck like AndrewH, you might have the option to go with a powered or non-powered (amplify the GPS signal before demodulation or demod w/out any amp), sport the money for the powered if its not too much extra. I've never used commercial pucks (maybe the all come powered, I'm not sure) but military pucks like this used to come in either pwr'd or unpwr'd configs so I'm guessing commercial version might as well.