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For 'f' in GHz and 'D' in feet, I always use Gant, dB = 20 log( f x D ) + 7.5

But I think that's for 55% efficiency. If the eff is 60%, that's 20log(60/55) better = another 0.75 dB. So let's make it

Gant, dB = 20 log( f x D ) + 8.25

20 log( 6 D ) + 8.25 = 50

20 log( 6 D ) = 41.75

log ( 6 D ) = 2.0875

6 D = 102.0875

D = 102.0875 / 6 = 20.39 ft = 6.21 meters (rounded, but it looks reasonable; hope it's close)

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15y ago

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