[TowerTalk] Site Elevation and TOA

Pete Smith N4ZR n4zr at contesting.com
Wed Jun 18 07:00:41 EDT 2014

One of the things I learned when inserting additional points in NED data 
is that it *is* possible to break HFTA by supplying too many points for 
it to work with - I just wish I could remember what the maximum number is.

73, Pete N4ZR
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On 6/18/2014 5:52 AM, Ian White wrote:
>> On 6/18/2014 12:07 AM, David Gilbert wrote:
>>> The HFTA terrain file is a very simple text file containing two
>>> columns of paired numbers (one for distance and one for elevation)
> and
>>> is trivial to edit.
>> Yes. When I was first learning HFTA, I generated a couple of radials by
>> tracing a line, picking elevations off of a terrain map.
>> 73, Jim K9YC
> All users should try creating a .PRO file from scratch at least once,
> because creating your own file gives far more insight into how HFTA
> actually uses its radial data. If you use only the SRTM data, your
> understanding will remain stuck at "consumer level".
> A couple of points that are in the manual somewhere, but might be
> missed:
> 1. HFTA doesn't require terrain heights at uniform distance intervals.
> It builds up the terrain profile by connecting whatever data points you
> have provided, using straight lines. For intermediate distances, HFTA
> will interpolate as required.
> This means a "flat terrain" profile can be created in just three lines:
> (measurement units), (height at zero range) and (height at maximum
> range) - for example,
> meters
> 0 87.1
> 4000 87.1
> Any height would produce the same results, so long as it's the same in
> both lines.
> 2. SRTM data often requires some editing to supply local detail that the
> radar didn't see - but YOU know exists, and so too did the old-time
> surveyors on horseback. So once again, you need to know how to edit a
> STRM-generated .PRO file to insert an extra line or two.  You can add an
> extra data point at any distance (provided that the distance is greater
> than the line before, and less than the line following). If the file
> already contains the maximum allowable number of lines, see 1 above to
> help you decide which of the other lines can be safely removed.
> Try it - you'll learn something.
> 73 from Ian GM3SEK
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