[Towertalk] Terrain Analysis

[Robert Shohet]

> For those who have played with the Terrain analysis
> programs - some questions.
>
> I have been developing elevation files for my QTH.
> The sample elevations files in YTAD/YT seem quite
> large in their distance intervals (100-200 feet).
> This may because of the use of regular topographical
> maps. Using DEM (Digital Elevation Map) files, I can
> get my intervals down to .01Km (33 feet) and go up
> from there. In fact, I use .01Km for the first .5Km,
> .05Km intervals to 1Km, and then .1Km intervals
> to 5Km which is where I stop.
>
> Am I working too hard at this?

Yes!

My suggestion to you - plot the distances where the elevation changes.

I have erratic terrain here in CT, so I use the topo maps to approximate the
actual heights ASL at points where the elevation actually changes.  The
better I have calculated the points and filled in the gaps, the better the
correlation between the predicted and actual antenna wave angles, patterns
and nulls.  So a plot of my terrain here to the West might be something like
0, 790  10, 775, 20 770, 60, 790, 100 740, 170 680, 240 660, 300 630, 500
610, 1000 500, 1500 450, etc.

I could split hairs even more, but I have probably captured 90% of the
relevant data for plot purposes.

If I had flat ground in the direction that I was modeling, I could probably
get away with 0  790, 20 790, 100 790, 300 790, 500 790, 1000 790, 5000 790,
etc.

The more data I included, the more useful and on-target the plots became.
But that was because I had previously excluded the small elevation changes
close in to the tower.

To satisfy your curiousity, try general plotting without much detail, then
try the method that I suggest and report back to net.

GL!

73

Bob KQ2M
>
> Neat to learn new things. Gives me an appreciation of the
> complexities involved in signal arrival.

BTW, with stacks and the ability to switch between them, you will experience
another order of magnitude of complexity (and usefulness!)