Good Morning Jim, and Dave, and all,
Jim, I have two expectations with you on this.
1. That you will show me the same patience and respect
as I and others have shown with your postings on various
topics, on different forums, and over a wide span of years.
2. That we both share a mutual desire for minimum misleading
statements and maximum technical accuracy in the data shared.
Those are my expectations, you are free of course to do what
you want. Overall, I think there is more agreement on many of
the points shared in this entire thread, than disagreement.
Now, please see below Jim ... TU!
On 06/22/2022 2:18 AM Jim Brown <jim@audiosystemsgroup.com> wrote:
>>On 6/21/2022 7:37 PM, Billy Cox wrote:
>>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?
>>Because as KK9A explained, it doesn't model interactions
>>between the two antennas, which can be considerable.
Jim, John/KK9A/W4AAA did not explain anything! John did
provide a link to the HFTA document which Dean created,
and I trust was peer reviewed before release. John also
then provided a partial copy paste, that was out of context
possibly to the topic at hand, more on that shortly.
Jim, I do not believe you had the opportunity to read the
actual document provided in the link due to the late hour?
If you had you would have found the following statements by
Dean ... copy paste follows of key points, all taken in whole
from the link John provided, anyone can confirm this as fact.
https://manualzz.com/doc/10293860/hfta---instructions
Page 1, second paragraph, titled PREFACE
HFTA is a ray-tracing program designed to evaluate the effect of
foreground terrain on the elevation pattern of up to four multi-
element HF monoband Yagis in a stack. See Chapter 14 in the 23rd
Edition of The ARRL Antenna Book for details about the theory
behind ray tracing and diffraction in HFTA.
For emphasis, I repeat: HFTA is a ray-tracing program designed to
evaluate the effect of foreground terrain on the elevation pattern
of up to four multi-element HF monoband Yagis in a stack.
Who made this statement? Dean Straw, N6BV
Page 2, last paragraph on the page, titled ANTENNA HEIGHTS
Once you’ve selected a terrain profile name, you will want to
choose the type of antenna and the number and heights of antennas
in a stack. Click on the Ant. Type or Heights box you want. A
new dialog box will open. See Fig 2. The default when you first
start HFTA is one 4-Ele. Yagi antenna, at 100 feet in height. Let’s
say that you want to specify three 4-Ele. Yagi antennas in a stack
at 90, 60 and 30 feet. You would place the cursor in the top left
text box and edit the 100 to be 90. Then you would edit the second
box to be 60 and the third to be 30. You can move the mouse or use
the Tab key to advance the cursor from box to box. Once you click on
OK, you might want to set the same heights for the next Terrain Files
box. The Copy buttons on the right side of the Height 4 boxes give
you a quick way of copying one row to another row. Click on the Copy
button you want and you will see the other two Copy buttons change
their labels to “To”. Click on the To button you want. By the way,
always specify a height for each Terrain —0 feet won’t work right.
Who made this statement? Dean Straw, N6BV
This forum does not allow graphics or attachments, but on the top
of page 3, we find labeled a Fig 2-Entering antenna types and heights
for each terrain file
... if HFTA is not to be used for stacks? Ahhhhhhh ....
Let walk together a bit further now please?
Also on page 3, second paragraph, titled OUT-OF-PHASE FEED
There is a useful feature in HFTA that earlier versions (such as YT)
didn’t have. You may choose to use out-of-phase drive to individual
antennas in a stack. You do this by appending an asterisk (*) to the
end of a height number. For example, in a stack at 90, 60 and 30 feet,
you might run the top 90-foot high antenna out-of-phase with the two
lower Yagis. Enter 90*in the top left text box. Although employing
out-of-phase drive is not often useful in terms of increasing the
overall performance of a stack of Yagis, sometimes it can cover high
angles that a stack or any single antenna cannot accomplish because
of a steep mountainous terrain.
Jim, how many times is the word 'stack' found in Dean's text above?
Finally for now, here is the complete copy/paste John referenced:
Beginning at the bottom of Page 3, and ending on the top two lines
on Page 4, titled A CAVEAT ABOUT CLOSELY SPACED YAGIS IN A STACK
The internal Yagi model in HFTA is a very simple mathematical model.
It does not compute interactions between individual Yagis in a stack
—HFTA assumes that each antenna is a “point source.” For antennas
stacked more than about a half wavelength apart this is not a problem.
For example, you should be cautious specifying spacings less than
about 20 feet on 20 meters (and proportionately scaled on other bands)
because of mutual-coupling effects between real antennas. Spacings
less about 20 feet on 20 meters will show a false increased gain in
HFTA, even though the real effects of interaction between the beams
will actually be to decrease the gain.
I am going to repeat this next sentence for emphasis, again these
are Dean's words, not mine ... For antennas stacked more than about
a half wavelength apart this is not a problem.
Jim, please help me reconcile the following two statements that I
have been accused of misleading others and not being technically
accurate:
S1: IT DOESN'T CALCULATE THE EFFECTS OF STACKING DISTANCE
AT ALL.
Incorrect, Dean does indicate changing heights changes results,
why else is there an entry box for up to 4 different heights?
S2: That isn't my opinion ... that's the word from Dean Straw, the
author of the program.
Incorrect, show me the direct quotes from Dean, using the same
document that John KK9A provided the link for that supports
either falsehood.
>HFTA is a very useful tool FOR WHAT IT WAS DESIGNED TO DO.
>Caps for emphasis. These actions come in the form of currents induced
>and impedances coupled between elements of the coupled antennas.
Jim, please re-read my posts, I agree with you, HFTA is very useful
when used properly with good data (think garbage in garbage out). It
like any other process, manual or software based, is also subject to
multiple errors, Dean mentioned several cautions on such risks and as
you have stated to others over the years, Read The Fine Manual.
>Those who are saying this are well-educated engineers. And Dean was
>the editor of the Handbook and Antenna Book when he developed HFTA.
>Ward Silver took the reins when Dean retired. I know both men, have
>worked extensively with Ward, and both are excellent engineers.
Jim, no where did I say anything contrary to above. Dean, I have never
met, but I have read many articles/posts from him. Ward and I actually
had dinner in Lebanon, TN many years ago as part of a group setting.
Both are fine gentlemen, and committed to helping others learn, agree?
There many excellent sources of wisdom on this forum, and not all of
them are engineers by trade or degree, many are, many are not. Your
work on audio/RF/pin is well respected, Jim Lux ditto, and Dave AB7E
has shared data as to the minimum discernable change in signal strength
that aligned very well with my real world data on the various bands.
(Those are just a few off the top of my head, there are MANY more)
Others have also commented on this thread as to the challenges of how
accurate are the results. I agree, especially when we back up and look
at all the possible points of error in the variables used.
Year after year we have all benefited from the wisdom shared from Frank,
W3LPL and Tim, K3LR ... who of their own choice have opened the doors
to what they have/are/and will learn by allowing us a ring side view
of their stations to become "real world experimental labs". That is so
cool, ditto for all those who teach at Contest University, TU to them.
My concern is two-fold ... first ...
Dean clearly said HFTA can be used with stacks, I do not see anything
otherwise in the cited material. I do see a concern, along with a solution
as to ensuring the spacing stays at least a half wave apart.
Thinking back to past Contest U, Dayton Antenna talks, etc ... I seem
to recall many slides that used HFTA to show how/why stacks work at
times, and at other times the low or high yagi might actually be better.
Were all of those presentations in error? Case in point ... we have
what Dean stated, what has been shared among peers, and then now we
have out of context statements that HFTA can't be used with stacks?
Something is wrong with this picture ...
Second, like it or not ... forum posts may outlive us all. Meaning
if someone reads that HFTA really is not useful for stacks, and that
statement is incorrect, how will they know unless it is challenged,
examined, and hopefully corrected. Jim, you are well known for doing
exactly that, again recall my two expectations in this forum post.
At CU this year, I answered some questions from newer contesters.
One, had already made an investment in tower/antennas/etc that probably
cost $10,000+. His question was "Why doesn't it play like I expected
or like so and so?"
Guess, what I told him Jim ... Hey, it's great you have made such a
large investment in hardware, now stop and invest time and money to
really understand how all that stuff out in your yard really works.
Please do that before you spend another dollar out there and then I
commended him for attending CU, but not to stop there, keep learning!
Another asked me where he could find information on the web, and I
said to use TowerTalk, and to also search the archives. He said he
didn't want to do that as he had read some of the posts, and to him
it sure seemed like questions from newbies were unwanted or in his
words they were "beat to death" for not knowing anything/everything.
I read a private email last night expressing a similar attitude on here
and I am not certain what was worse, the disappointment or the reality
that what he posted is actually true at times, this thread as an example.
Guys and gals, we can either sit here and B & W among ourselves while
the next generation 'tunes us out', or we can figure out ways, yes
even ways that drag us out of our comfort zones, and engage them.
(Data point, earlier this year I passed the 50 year point of having
my ticket, and add another roughly 10 years as a SWL in DL 1st and
then the US as my father was a career Army officer, so we moved a lot)
That data point does not prove a thing, other than somehow I am now
old, that I am still "bit by the bug", and while I have experienced
many changes, the reality is the future will require more of the same.
>Software like NEC can model antenna interactions, producing a full 3D
>pattern over a flat earth or in free space, but it cannot model terrain,
>and there's no way to transfer that to HFTA in a meaningful way, because
>each of the two antennas interact differently with the terrain depending
>on their 3D location with respect to that terrain. FAR more complex
>software is required to that, the terrain data must be plugged into it.
Jim, once again we are in agreement as one who started with punch cards
in junior high to design a dipole, to ELNEC, then EZNEC, and also some in
our group had Brian, K6STI's software, Roy has been a great mentor, as
has Dan, AC6LA with both of his software packages too. I am fully aware
as to NEC2/NEC4/and now NEC5 and the file changes needed with each
engine, and also with MININEC verses NEC to explain some of the Moxon
model mysteries. Thinking back to my 1st 8088 w/o a math chip to what is
sitting on my study desk today and the speed it models at, wow ... simply wow.
>One program that MIGHT be useful is called Hobbies.
Yes, I agree Jim ... and am hopeful that will be true, as well there
are several modeling software options used in EU, those might be worth
a closer look in the days ahead. For now, as Ron posted, "One without the
other is a waste of time" may the best that we can do, recognize the
known traps, avoid such, and share/teach/help others to learn the same.
My "milk carton use by" date has long since expired as a contester, DXer,
or whatever and that's OK. What I enjoy most now is seeing others enter
into the game, learn how all this really works, and then realize their
potential while having as much fun as possible along the way!
Toward that goal, my apology for the length of this post, if I sense
something is amiss, like you do Jim Brown, I am going to question it
and at the worst learn something new, and at the best correct the data
so those who are still learning, will learn in an accurate manner.
73 to you Jim, de Billy, AA4NU
>73, Jim K9YC
________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|