The practical range of a VHF radio contact depends primarily on your altitude and the altitude of the ground station. Because VHF propagates quasi-optically (in straight lines), the range is limited by the radio horizon—the farthest distance at which a line of sight can be maintained between your antenna and the ground station antenna.

A simplified formula for radio horizon distance is:

For practical purposes, aviation instructors and pilots use an even simpler rule of thumb:

Let's work through an example. If you are flying at 5,000 feet altitude:

√5,000 ≈ 70.7 1.23 × 70.7 ≈ 87 nautical miles

So at 5,000 feet, you can expect to maintain two-way VHF radio contact with a ground station at approximately 87 nautical miles away (assuming the ground station antenna is at or near sea level).

If you climb to 10,000 feet:

√10,000 = 100 1.23 × 100 = 123 nautical miles

At 10,000 feet, your range increases to roughly 123 nautical miles.

These calculations assume ideal conditions: clear line of sight, no terrain obstruction, and no interference. In practice, range may be slightly less if high terrain between you and the ground station blocks the direct line of sight.

It is important to note that this range formula applies to both transmission and reception. If you are at 5,000 feet and a distant ground station is also at significant altitude (say, on a hilltop at 2,000 feet), the combined range is greater than if the station were at sea level. This is why communication with high-altitude ground stations is often possible from farther away.