I strongly suspect that for flat or uphill sloping terrain that it isn't
necessary to carry the terrain profile out very far, and 3,000 meters
may be fine for that. I live on terrain with a rather significant slope
to the east (about 15% for several hundred meters and then 4-6% for
about 7 miles after that), however, and HFTA definitely shows the effect
of a mountain range at least 15 miles away. That would seem to make
intuitive sense ... a terrain feature that far away wouldn't show up on
HFTA if you didn't have a very low takeoff angle to begin with.
73,
Dave AB7E
On 8/16/2011 12:34 PM, Pete Smith wrote:
> Jim, I always test results in HFTA, and compare the theoretical patterns
> over flat ground with my actuals. I also use MultiNEC for modeling
> (wish I had the NEC4 engine, but hey...), and where appropriate I apply
> the notches and reinforcements from HFTA to the MultiNEC patterns. My
> terrain is relatively flat, though, so I feel comfortable not carrying
> my terrain profiles out over 3000 meters.
>
> 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,
> spots at telnet.reversebeacon.net, port 7000
>
>
>
> On 8/16/2011 11:55 AM, Jim Brown wrote:
>> On 8/16/2011 7:35 AM, Pete Smith wrote:
>>> For example, if I model against
>>> ground, and put the antennas at heights of 50 and 100 feet, my 14 MHz
>>> vertical pattern is very broad and clean, with no second lobe below 35
>>> degrees or so.
>> Don't forget that all of this can be QUITE dependent on the terrain in
>> the region up to at least five miles from your antenna. N6BV's HFTA
>> software allows us to model this, using data readily available on the
>> internet. That software comes with the ARRL Antenna Book, and is worth
>> the cost of the book.
>>
>> 73, Jim Brown K9YC
>> _______________________________________________
>>
>>
>>
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