[Towertalk] Terrain Analysis

[Bill Tippett]

N0FP wrote:
>If you figure a better way to grab the data, let me know.  I'm interested
too.

        If you know someone who has any version of Topo USA, this is 
very easy to do.  You first find your location, then select a point
in the desired azimuth direction about 2 miles away, and it generates
a chart showing elevation changes over that distance.  I only enter
significant changes to minimize the data input.  For an antenna 200'
high, looking out ~2 miles will work for takeoff angles down to ~1 
degree.  If you want lower than that, solve the following for H:

Tan (TOA) = H/D, where H is height of highest antenna, D is most distant 
reflection point, and TOA is takeoff angle in degrees.

If my highest antenna is 200', and I want refelctions down to 0.5 degrees,
I need to plot terrain out to:

D = 200' / (tan 0.5) = 22,918' or 4.34 miles.

                                                73,  Bill  W4ZV