Something about communication range

Ever wondered about the claims some manufacturers put on the box? 10, 20, 30, 40 kilometers between two handhelds? Did you ever achieve it?

Probably not, and I’ll try to explain why by using a simple example.

Before we go any further we’ll going to assume a few things.

1. Both persons holding the radios are 1.90 meters (about 6″2) tall
2. Both radios are identical in every respect
3. We use the 2 meter amateur band (VHF) and 5 Watts output
4. There are no obstacles between the two radios
5. Nothing above ground affects the signal in a negative nor positive way
6. There are no special band conditions

Under these circumstances, what is the maximum range?
a) up to 6 Km
b) up to 10 Km
c) up to 20 Km

The answer is: up to 6 Km, give or take a few meters (the exact number is 5.7 Km). The reason why…