# [CQ-Contest] Contest QTH

Pete Smith n4zr at contesting.com
Sun May 23 06:44:19 PDT 2010

```I hope that Dean will chime in here, because I recall an e-mail
conversation a few years ago in which he said he felt that About 3 miles
was a practical limit.  I once built a terrain file that had too many
points for HFTA to process, which suggests to me that you need a
compromise between the range covered and the amount of detail in the
profile.

My trig is way too rusty to attempt the math, but if you start with an
antenna at a given altitude, go out 15 miles and identify a point that
is maybe 500 vertical feet above that plane, and draw a line between
them, as well as a horizontal line (we're talking flat earth here
hi)from the antenna to the obstruction, what angle above the horizontal
will just clear the ridgeline?  I know the number is pretty small, just
not *how* small.

73, Pete N4ZR

The World Contest Station Database, updated daily at www.conteststations.com
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On 5/23/2010 12:47 AM, David Gilbert wrote:
> Hi, Pete.
>
> I don't think there is any kind of formal limit in HFTA.  The terrain
> slopes rapidly down eastward from my QTH at roughly 15% for about a half
> mile, maybe 8-10% after that for a couple of miles, and then about 4%
> for the next five miles.  After that it starts sloping gently upward for
> a few miles before hitting a mountain ridge line about 15 miles away
> that is just a bit higher than my QTH.  I've compared terrain files with
> and without that distant ridge line and the impact is definitely
> noticeable at low angles.  Granted, HFTA says my particular QTH puts out
> a lot of energy at very low angles (the major peak is at 2 degrees), so
> maybe 4,000 meters is a practical maximum horizon for a more typical
> terrain, but I don't think the program constrains itself to any
> particular distance.
>
> 73,
> Dave   AB7E
>
>
>
> On 5/22/2010 2:44 AM, Pete Smith wrote:
>
>> HFTA only uses terrain out to about 4000 meters.
>>
>>
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```