HFTA is a terrain analysis program developed by Dean Straw, N6BV, of ARRL.
It comes free with the ARRL Antenna Book and includes a program called
MicroDem that is used to capture and process USGS terrain elevation
information from the Internet. The theory is that terrain has an effect on
antenna gain. Most of you are familiar with the fact that the gain of a
dipole over real ground is increased by about 3 dB over a dipole in free
space. The difference is caused by part of the wave bouncing off the ground
and reinforcing the wave at the main angle of radiation. Many of you also
know that if a big hill is too close to your QTH, your signal in that
direction is going to be weak. HFTA takes these concepts much farther by
analyzing the wave effects caused by terrain features out to a radius of
about 4400 yards. The results from HFTA have been compared with real-life
experiences and the correlation seems to be pretty good. In my case, HFTA
predicted that one tower location on my property would be 2-3 dB better than
another about 200 feet away and down a hill. That confirms my experience in
real, on-the-air comparisons.
If the terrain varies a lot, as it does in the hilly country where I live,
an accurate GPS is necessary in order to get the exact location of the
tower. In some cases, you can do OK by interpolating from a map, but in my
case a difference of 20 feet or so can make a big difference in the results
reported by HFTA. This is because a small shift in the tower location can
bring different terrain features in and out of the radiation window. I use a
Garmin GPS V, which has accuracy to 3 meters or less. It can average any
number of readings, which will get accuracy down to three feet or so. It
cost about $350, and I use it a lot in my car -- it has downloadable maps
and very sophisticated autorouting.
73, Dick WC1M
> -----Original Message-----
> From: Don Havlicek [mailto:n8de@thepoint.net]
> Sent: Friday, September 17, 2004 12:05 AM
> To: Jim Brown
> Cc: Tower Talk List
> Subject: Re: [TowerTalk] GPS receivers
>
>
> I'm almost afraid to say it .. .but .... it might help find
> TRUE NORTH!
>
> Don
> N8DE------ ducking to avoid the FLAMES.
>
>
> Jim Brown wrote:
> > On Thu, 16 Sep 2004 22:50:40 -0400, Steve wrote:
> >
> >
> >>HFTA
> >
> >
> > Aw cummon -- cut the acronyms -- what the heck is HFTA? If people
> > understood your question you might get more and better answers. :)
> >
> >
> >>The Help recommends use of a
> >>GPS receiver to determine lat/long for the site under analysis
> >
> >
> > That's kind of like going after a gnat with an elephant
> gun! There are
> > a
> > LOT cheaper ways to figure out lat/lon coordinates (like
> looking at a
> > map, visiting various mapping sites on the internet, etc.).
> >
> > What does this software do with the coordinates once it gets them?
> > Figure out great circle headings? They are an occasionally
> useful toy,
> > but they are not cheap -- you can buy a nice ham rig for
> what they cost.
> > I have an old Magellan that plugs into my Handspring and gives me
> > coordinates when I am traveling. If you WANT to own a GPS, fine.
> > Otherwise save your money for something you really need.
> >
> >
> > Jim Brown K9YC
> >
> >
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers",
> > "Wireless Weather Stations", and lot's more. Call Toll Free,
> > 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
>
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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