HFTA is useless if you dont also incorporate other station data during your
analysis besides the info the program needs to function:
1-A list of bands you are planning to operate using horizontal yagis or
phased wires.
2-A list of antennas you are considering along with their modelled forward
gain in dbi.
2-Which continents or cities do you wish to optimize in this effort ?
3-What are your goals for each band and the areas youve selected for your
horizontal antennas ?
4-The prevalent takeoff angles needed to reach your selected target areas
on the bands youve selected. This info was initial present by N6BV years
before HFTA.
5-Once youve identified an area of pronounced performance degradation (null
/cancellation) on a particular band, what steps are you willing to go to in
order to overcome this ?
Raise or lower the antenna, add elements, add or remove stacked
antennas, or place the antenna elsewhere.
DIRECTION + YOUR TERRAIN + ANT HEIGHT + ANT PATTERN & GAIN + PROPAGATION
ANGLES = HFTA RESULTS for comparison.
Ive used HFTA to model similar antennas and then measured on-the-air
performance of my station to a nearby hill to NEW ZEALAND for my QTH..
HFTA reported 50db difference between similar antennas at 30ft and at 90ft
to NEW ZEALAND pointing over a 80 foot hill located 1000ft from my QTH.
The on-air difference matched the HFTA modelling results.
-Charlie N1RR
On Mon, Jan 21, 2019 at 8:05 PM Bob Shohet, KQ2M <kq2m@kq2m.com> wrote:
> There is another limitation as well....
>
> While K6STI’s YO program allowed you to select from a list of “stock”
> antennas, or put in the actual measurements of your own, and THEN stack
> them, over ACTUAL terrain,
> HFTA does not allow you to specify an exact antenna – only a “generic” one.
>
> That might not sound significant until you realize (by doing the actual
> modeling) that the “best” heights for a given wave angle on a particular
> band are actually DIFFERENT for different antennas. And when you stack a
> pair or three of the same DIFFERENT antenna, the best heights for a given
> wave angle change even more and they have DIFFERENT lobes and patterns as
> the terrain changes from flat to something else.
>
> My stack of Hygain HG105CA’s or HG155CA’s or HG205CA’s produces different
> patterns and lobes at different angles than a different 5L beam would.
> Sometimes the differences are LARGE at a give wave angle. Certainly this
> is different than one would expect without modeling them. HFTA will not
> differentiate between different antennas – so what you see for lobes may be
> incorrect – better or worse.
>
> Likewise, K6STI’s fabulous program did not have a graph or chart that
> showed the % of signal at a given wave angle.
>
> So what to do? The answer of course was simple – USE BOTH programs -
> HFTA and K6STI’s suite of programs! Each for their best and most useful
> attributes.
>
> I learned a lot more and developed a better 3D understanding of different
> antennas, transmit and receive wave angles and the effects of stacking by
> using BOTH programs. And by changing the direction of the Terrain file and
> replotting the actual heights about sea level in each direction for each
> antenna and stacking combination, I learned how even the smallest terrain
> changes could have ENORMOUS impacts on the best stacking heights and how
> the best stacking heights changed yet again depending on the SPECIFIC
> antenna that I was plotting. Only through modeling and using BOTH programs
> did I discover all of these valuable and unusual characteristics and
> information that were essential to maximizing my 10, 15 and 20 meter
> signals.
>
> The modeling programs are remarkably accurate and they have had profound
> influences on my level of understanding and the quality of my signal. For
> me, they have been the most effective station additions that I could
> possibly buy!
>
> For those of you who are still skeptical, I can say with complete
> confidence that there are virtually NO big contest or DX stations that have
> been built in the last several decades without extensive modeling of
> antennas and/or terrain for their qth. It’s one of the reasons why they
> are LOUD!
>
> 73
>
> Bob KQ2M
>
>
>
> From: jimlux
> Sent: Monday, January 21, 2019 6:20 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] The Value of HFTA
>
> On 1/21/19 11:33 AM, Jim Brown wrote:
> > On 1/21/2019 11:23 AM, Edward Sawyer wrote:
> >> One thing that HFTA does NOT do well is answer the question about
> >> stacking
> >> from a "max gain" perspective. EZNEC will tell you the best design for
> >> stacking yagis for max gain in a direction however HFTA will tell you
> >> what
> >> the right height for those yagis are or if the stack is even the
> >> strongest
> >> signal under typical approach angles.
> >
> > Right. HFTA models the performance of individual dipoles used alone, not
> > in combination. When you select a Yagi, it simply adds gain.
> >
>
> Correct me if I'm wrong, but I think it also changes the effective
> vertical beamwidth of the point source radiator (in proportion to gain
> or sqrt(gain) or some rule). that is a 2.15 dBi dipole has a vertical
> pattern that is uniform gain, but a 10 dBi Yagi has a vertical pattern
> with some significantly smaller vertical height.
> _______________________________________________
>
>
>
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