[TowerTalk] HFTA and Delorme data bases

Dean Straw n6bv at arrl.org
Wed Sep 12 11:19:20 EDT 2007

I have placed a new set of operating instructions for the use of MicroDEM to
generate HFTA terrain profiles on the ARRLWeb site:
http://www.arrl.org/notes/9876/HFTA.pdf. These instructions reflect changes
that have been made to the USGS and other download sites and they reflect my
new point of view that using DEMs (the old 7.5-minute topo "quads") is
generally more accurate than using NED "seamless" data.

Yes, getting the USGS topo data files for MicroDEM to use can be somewhat
intimidating at first. You've really got to follow the instructions
explictly. But doing it electronically by DEM download really does beat the
heck out of creating topo terrain data by reading it off a Delorme topo
screen and punching it in point-by-point. I figure it takes about 10 to 15
minutes to identify and then download up to four USGS DEM (7.5 minute
"quads") and merge them, and then about 1 minute to have MicroDEM create 71
terrain files automatically in 5-degree increments.

I'd guess that it would take about the same amount of time to generate a
terrain file at a single azimuth using Delorme Topo USA. As the saying goes,
of course, "Your mileage may vary."

73, Dean, N6BV
Senior Assistant Technical Editor, ARRL
Editor, The ARRL Antenna Book
Author, HFTA

> Date: Tue, 11 Sep 2007 21:29:43 -0500
> From: "William B. Stacy" <wstacy at wildblue.net>
> Subject: [TowerTalk] Delorme data bases
> To: <towertalk at contesting.com>
> Message-ID: <000001c7f4e4$cd3f7f80$6401a8c0 at BILLSONY>
> Content-Type: text/plain;	charset="us-ascii"
> I have been using Delorme Topo USA for years, both when I was in
> Wyoming and
> here in Oklahoma.  (I never could figure out how to make MicroDEM
> play.  Too
> many interlocking downloads, I guess.)
> In Topo, you can set your QTH and then draw a radial toward a point of
> interest such as EU.  Then you can get a plot of the terrain in that
> direction.  The resolution is really, really fine.  This sure beats the
> daylights out of using a USGS topo map and a ruler to work out
> the contours.
> Beyond a certain point, Topo gives distances in miles, so I set
> up an Excel
> spreadsheet to convert to feet.  (I could have used meters, I
> know.)  Then I
> copied the Excel data and pasted it in a Notebook file that I
> saved with the
> extension .pro.
> Beware: HFTA is addictive.  ;-)
> 73, Bill, N5TU
> Message: 4
> Date: Tue, 11 Sep 2007 18:25:40 -0400
> From: "Byron Lichtenwalner" <w3wkr at verizon.net>
> Subject: [TowerTalk] Delorme data bases
> To: <TowerTalk at contesting.com>
> Message-ID: <01bf01c7f4c2$b024c120$6401a8c0 at ann2>
> Content-Type: text/plain; format=flowed; charset=iso-8859-1;
> 	reply-type=original
> Friends
> I would like to use MicroDEM/HFTA to do some analysis of my site.
> Have any of you used Delorme Topo USA to do this, and if so with what
> success??
> Byron, W3WKR
> ------------------------------

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