Space wave propagation can be achieved in the following 2 ways:
1) LOS Communication
2) Satellite Communication
Consider a TV antenna OP of height h. The transmitted signal cannot be received beyond points $R_1$ and $R_2$.
$OR_1$ and $OR_2$ are maximum distance from the antenna.
let $OR_1 = OR_2 = d$
from $∆PCR_1$
$CP^2 = PR_1^2 + (CR_1)^2 \\
(R + h)^2 = PR^2 + R^2 \\
In ∆POR, \\
PR_1^2 = h^2 + dr^2 \\
(R + h)^2 = h^2 + dr^2 + R^2 \\
R^2 + 2hR + h^2 = h^2 + dr^2 + R^2 \\
dr =\sqrt{2 R h_r} \text{(for transmission)} \\
\text{Similarly,} d_R =\sqrt{2 R h_R} \\
d = dr + dR$