[TowerTalk] Stacking Tribanders
David Gilbert
ab7echo at gmail.com
Wed Jun 22 00:51:28 EDT 2022
That long rant doesn't change anything, I'm afraid. Nobody is trying to
trash anyone, but it doesn't serve you or anyone else for you to keep
insisting something that isn't technically accurate. This is an
educational forum and if you want to believe something that isn't true
that's your business, but don't expect everyone to sit by while you
mislead others.
Just look at your rant below. It almost exclusively talks about HFTA's
terrain analysis capabilities. That isn't the point here at all. HFTA
has been shown to work fine for most terrain studies ... excellent in
most cases as that's what it was designed to do. But that doesn't carry
over to stacking calculations. You keep acting like they are the same
... they are not. HFTA doesn't have a "tolerance for error" on stacking
distance ... IT DOESN'T CALCULATE THE EFFECTS OF STACKING DISTANCE AT
ALL. That isn't my opinion ... that's the word from Dean Straw, the
author of the program.
Dave AB7E
On 6/21/2022 9:08 PM, Billy Cox wrote:
> 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 at 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 at 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 at 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 at 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 at 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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