Powering a modem over extreme distance (~2k feet)
2000' of 14 guage wire = 4000' * .003 Ohms per foot = 12 Ohms.

Voltage drop at 1.5 amps is going to be 18 volts, you would have to feed it with 18+12, which isn't a good option.  

12v*1.5a=18watts, 18 watts / 75% efficient switcher/transformer = 25watts / 120v = 0.2 amps.

A better option would be 120v, which would calculate to around 0.2 amps, for a 2.4 volt drop, which could work.  However, protecting your electrical system from lightning gets difficult with two systems operating 2000 feet away, yet connected.  If it is fiber, isolating the modem may be best.  

Note that the 120v neutral is probably just as dangerous as the hot at these kinds of distances.

All in all, consider yourself lucky that you can get cable internet in a rural area.