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Need help - there is math invovled

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imbadatthis
Need help - there is math invovled

howdy,

Trying to self study for an exam. Im wondering if anyone can be kind enough to provide me with either:
1- link to an online calculator that I could use to verify my answers
2 - be kind enough to tell me if im correct or not.

need to find out minimum height required for two antennas that are 60km a part. with a 30m tree 20 km away from one of the antennas.

the freq used is 8 Ghz. and we are assuming K = 4/3

I calculated H = 0.078 (20) ( 40) / (4/3) = 46.8 Meters. this is enough for earth's bulge.
add the 30m tree = 76.8

calculate 1st fresnel zone : 17.32 * sqrt[(1*20 * 40)/(8*(20+40))] = 22.36

add em all up = 99.16 m , is minimum height.

is this correct?

p.s: sorry if this is not the place to ask, its my first day ...