"nobody" wrote in message ...
100 m W can 7 Km

according http://uk.youtube.com/watch?v=xNFg8l5tjDI

I draw conclusion from the movie at 0.22 second from the above movie


1000 m W = 1 W

1 W can reach 7KM * 10

5 W = 7KM * 10 * 5

= 350 KM the signal still cannot reach the AO 51 satellite which is
850 Km away from the earth.


to reach AO 51 the power required at least 12.5 W

7KM * 10 * 12.5
=875 KM


is my calculation correct?


raw transmitter power is only one factor, you have to also consider the
antenna gain, receiver sensitivity for the different modulation used,
bandwidth, and noise. The biggest factors in this case are probably the
modulation type and noise. with ssb or even nbfm you are dealing with a
much narrower band signal than 802.11 that hops all over a wide bandwidth.
This lets the receiver pull the signal out better. Also the ssb or even
nbfm is easier for the human ear to copy through noise, and cw is even
better, but the access points have to deal with separating out the frequency
hopping digital data from all the other digital data noise on the same
frequencies... and if noise takes some of it out it is much less forgiving
than the low data rate human ear and brain.