Talk:Radio horizon

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16 Jun 2005, Boon Phing write: I think the conversion here is more for optical horizon rather than radio horizon. aren't we suppose to use r = 4/3 r0 for earth radius?

then

D [NM] = 1.23 * sqrt(H [ft]) <= radio horizon

instead of

D [mi] = 1.23 * sqrt(H [ft]) <= optical horizon

[edit] ===========================================================

someone wrote: "GF: I believe that the conversion here from ft to meters is wrong. Should have taken the square root of the conversion factor?"

I agree.

Horizon (mi) = 1.23 * sqrt(Height (ft));

take an antenna 100 ft high. sqrt(100)=10; Horizon = 12.3 miles.

Horizon (km) = 1.6 km/mi * 1.23 * sqrt(3.28 ft/m) * sqrt(Height (m));

1.6 * 1.23 * 1.8113 = 3.5646384... chop precision, to get

therefore Horizon (km) = 3.56 * sqrt(Height (m));

also, "The ARRL Antenna Book gives a constant of 1.415 for weak signals during normal tropospheric conditions."

strangely, the ARRL Handbook condradicts this: 1.15 is the factor quoted there (page 21.20 of the 1999 edition.) so which is correct? Waveguy

[edit] Adding up horizons

We were learning this thoery at college today and a question came up that could not be answered: Why do you add the horizons of the two Antennas, if Antenna A has a horizon of 8 miles and the second 10 miles, why can they be more than 10 miles apart? How does the signal get from the horizon of the first (say 8 miles) and arrive 10 miles farther at the second atennna? --Crossmr 16:09, 18 April 2006 (UTC)