Several of you must just like to b**** when ever a
younger/newer ham asks questions to learn something.
"Go read about it, learn it", and so when they
do using an "approved" source (ARRL publications,
including HFTA) then some now claim to be experts
and trash others when someone tries to actually
learn/build/use/enjoy the technical side of things.
Dean warned about possible errors, what else could
he do? I also mentioned that in a previous post.
Dean did not state HFTA was "virtually useless" for
modeling stacks over terrain did he? No, what he did
state was to be very careful in specific situations.
Yes, I have used HFTA, and prior to that we used a
similar package from K6STI for many years. I have
compared the software predictions with real world
results, and more time than not, it does provide
useful data. Notice I said useful, meaning much
better than ham lore or no information at all.
Perfect? No, again ... but that may also be true as
to the other data used in these HFTA calculations?
Case in point? Let's chat about how accurate is
the terrain data? What if there is large building
at a reflection/refraction point, or nearby, or
... or ... wait ... do we have to throw all HFTA
results out for even single antennas?
Anyone care to debate (I do not) the real world
impact on seasonal terrain foliage at HF bands?
Or how accurate really is your x element yagi as
compared to the gain stated with the HFTA models?
Or do we forget the optimum wave angles in HFTA are
averages, so at one specific time, are not very
accurate, and yet we use it for station planning.
Or the W4-TN profile ... is that accurate for
west TN, middle TN, or east TN? Well?
Or interactions with other antennas, that HFTA
cannot accurately (nor was it designed to take
into consideration) predict what the pattern is?
Do we toss HFTA for interactions? Well?
A practical option is to do what Ron stated, use
HFTA and EZNEC as a way to usefully (note I did
not say absolute accuracy) crosscheck results.
As in the old "trust, but verify" many of us
have used daily in other settings.
At the end of the day, this comes down to the
probability of error and what level of tolerance
(as in inaccuracy) one is willing to accept.
My doctoral chair cautioned that without reliable
and repeatable data, you only have an opinion, and
that everyone has one or more, but such does not
mean an opinion is credible without proven evidence.
So perhaps we need to ask Steve, K7LXC to add a tag
line to remind all of us, in the absence of reliable
and repeated data, we are just a bunch of old farts
trying to out-opinion the last opinion offered? hihi
Here's a closing "opinion" ... why don't together
we make TowerTalk a safe place for any person with
an interest in learning about antenna/towers/safety
to come here and post and not regret doing so ...
73 Billy, AA4NU
> On 06/21/2022 9:56 PM David Gilbert <ab7echo@gmail.com> wrote:
>
>
> Not sure how many times it needs to be said, so just go back and read
> KK9A's post.
>
> But in a nutshell, HFTA is an extremely valuable tool for terrain
> assessment and deciding how high to put your antennas. It is virtually
> useless for deciding on stacking distance because it was never intended
> to calculate that, and it will absolutely give you wrong results for
> close spacings. You can prove that for yourself simply by running
> various iterations.
>
> Dave AB7E
>
>
> On 6/21/2022 7:37 PM, Billy Cox wrote:
> > Dean stated in the documentation that there are
> > known 'traps' with the methodology used. As in
> > what happens to the reported gain when the ants
> > are too close ... cautions as to moving each of
> > the antennas a foot or two higher/lower to also
> > detect false results. Like any tool, physical or
> > software based ... used properly, it's useful,
> > used improperly, well we all know this answer.
> >
> > Or is Dean wrong also? Did the ARRL make an error
> > by including the software (with instructions and
> > stated limitations) as part the ARRL Antenna Book?
> >
> > So outside of the cautions Dean shared, and used
> > with other methods (EZNEC/etc.) why would one not use
> > HFTA as a useful software tool for stack planning?
> >
> > "That's just plain wrong" B-) B-) B-)
> >
> > 73/bc/NU
> >
> >
> >> On 06/21/2022 9:17 PM David Gilbert <ab7echo@gmail.com> wrote:
> >>
> >>
> >> Funny ... Ron privately answered me to thank me for the correction.
> >>
> >> I never said that HFTA wasn't extremely valuable. I used it when
> >> designing my station to determine the optimum heights for my antennas
> >> given my terrain profile ... at least within the physical limits of hwat
> >> I could afford.
> >>
> >> What I said was that HFTA is of no use in determining optimum stacking
> >> separation, and I stand by that statement.
> >>
> >> Dave AB7E
> >>
> >>
> >>
> >>
> >> On 6/21/2022 6:43 PM, Billy Cox wrote:
> >>> Dave G. ... did you miss or ignore this line of Ron's reply?
> >>>
> >>> "One without the other is a waste of time."
> >>>
> >>> Ron is correct, neither program provides a complete answer,
> >>> as both have known limitations. On the other hand, Ron is
> >>> quite the fast learner, as demonstrated by the excellent
> >>> station he has built, with scores that support his planning.
> >>>
> >>> 73 de Billy, AA4NU
> >>>
> >>>> On 06/21/2022 3:48 PM David Gilbert <ab7echo@gmail.com> wrote:
> >>>>
> >>>>
> >>>> That's just plain wrong. That's using HFTA to determine optimum height
> >>>> above ground ... not optimum stacking distance (i.e., separation). They
> >>>> are NOT the same thing. HFTA does NOT properly calculate anything based
> >>>> upon stacking separation.
> >>>>
> >>>> Dave AB7E
> >>>>
> >>>>
> >>>>
> >>>> On 6/21/2022 11:23 AM, Ron WV4P wrote:
> >>>>> HFTA should Always be used to try to optimize stacking distance.
> >>>>> It shows the nulls and enhancements created by Your Terrain, and how
> >>>>> to exploit and or cover them. Then you can use another program, like
> >>>>> EZNEC to calculate the stacking gain as a function of stacking
> >>>>> distance based on the HFTA data.
> >>>>>
> >>>>> One without the other is a waste of time.
> >>>>>
> >>>>> HFTA tells you where to put the antennas.
> >>>>> EZNEC tells you what antennas to put there.
> >>>>>
> >>>>> Ron, WV4P
> >>>>>
> >>>>> On Tue, Jun 21, 2022 at 1:00 PM David Gilbert <ab7echo@gmail.com> wrote:
> >>>>>
> >>>>>
> >>>>> HFTA should never be used to try to optimize stacking distance.
> >>>>> It
> >>>>> simply does not actually calculate the stacking gain as a
> >>>>> function of
> >>>>> stacking distance like EZNEC would.
> >>>>>
> >>>>> 73,
> >>>>> Dave AB7E
> >>>>>
> >>>>>
> >>>>>
> >>>>> On 6/21/2022 10:34 AM, sawyered@earthlink.net wrote:
> >>>>> > HFTA kinda sorta calculates stacking properly. It seems to
> >>>>> assume you get
> >>>>> > the optimum 2.7db stacking gain whether the spacing is optimum
> >>>>> or not. And
> >>>>> > it draws the HFTA ray from the center point between the 2. So
> >>>>> it would
> >>>>> > calculate a 2 high stack of 20M yagis having an added 2.7db of
> >>>>> gain even if
> >>>>> > they are stacked only 20 ft apart and will draw the enhanced ray
> >>>>> from the
> >>>>> > midpoint between the 2 yagis.
> >>>>> >
> >>>>> >
> >>>>> >
> >>>>> > Ed
> >>>>> >
> >>>>> > _______________________________________________
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