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Answer:

In the transmitting and receiving antenna, radio frequency line of sight is defined by FZ which are in the ellipse shaped areas between any two radios as shown in picture.
FZ can be calculated in mtr and fts as follows:

$$ r _{ \text{(in meters)}} = 17.32 \sqrt{ \frac {d _{\text{(in Km)}}} {4f _{ \text{(in GHz)}}} } $$ $$ r _{ \text{(in ft)}} = 72.05 \sqrt{ \frac {d _{\text{(in miles)}}} {4f _{ \text{(in GHz)}}} } $$

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