[CQ-Contest] Contest QTH

[Pete Smith]

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
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com


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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