How far a signal really goes
At 145 MHz the signal travels in a nearly straight line, so the radio horizon applies: about 4.12 × √h kilometres for an antenna at h metres. A handheld held at 1.5 m sees roughly 5 km of flat ground; a 10 m mast about 13 km; a 100 m tower about 41 km; a repeater on a 300 m hill about 71 km. Between two stations you add the two figures, so a mobile at 1.5 m talking to a repeater at 300 m can in principle work over about 76 km.
Free-space path loss at 145 MHz is about 95.6 dB over 10 km and 109.6 dB over 50 km. A 5 W handheld with a modest antenna delivers a signal of about -59 dBm at 10 km in free space, far above what a good FM receiver needs (roughly -115 to -120 dBm), so on a clear path the limit is not power but the terrain.
Why hills and buildings matter more than watts
Doubling the power adds 3 dB, while a ridge in the path can cost 20 to 30 dB or more. At 2 m the diffraction around hills is better than on UHF, which is why VHF often covers a valley better than a higher band from the same site. Trees and buildings add a few dB to tens of dB near the receiver; indoors, expect a clear drop. Test your own site on the coverage map: the shadows behind each hill are drawn from elevation data.
Getting the most from 2 m
Use a vertical antenna as high as you can, keep the cable short or use a low-loss type, and prefer a hilltop to extra power. A handheld with a rubber antenna has a gain close to 0 dBi or lower; a mobile whip or a rooftop antenna adds several dB and, above all, height. For links beyond the horizon, see line of sight versus diffraction and plan repeaters with repeater coverage planning.
