An equation that I leave in my HP calculator interrelates the important
parameters.

T = take-of-angle (up from horizon)
D = distance in Mm (40 Mm is all of the way around the earth)
H = virtual height of ionosphere in km

Calculator is using angles in degrees.
Single hop

Cos(T) / Cos(T + 4.5*D) = 1 + H/6366

F2 H for 40 degrees north is between about 250 and 370.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Ken Bessler" wrote in message
news:VEmag.22577$4H.10017@dukeread03...
Lets assume a single hop 40m signal from 400 miles away. What
elevation angle does it arrive at? Both stations are using inverted V's
at nominal height. There are no large bodies of water in between.

Daytime and/or nighttime.

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73's de Ken KG0WX -