[TowerTalk] HFTA first impressions

[Bob Farkaly]

By coincidence, I spent the afternoon doing the same sort of "stuff".
The documentation is incomplete and, in some cases, simply incorrect.
Nevertheless, I was able to generate all the reports and graphics I was
looking for. The terrain plot overlaid with the TIGER data is cool to
look at, but the value of seeing roads is questionable.

The software bits and pieces are what we refer to as a "kludge" rather
than an integrated product.

I would not recommend this approach to anyone without great familiarity
with Windows file structures and without a good grounding (no pun
intended) in antennas and propagation.

Bob, K9RHY 

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Lux
Sent: Sunday, November 09, 2003 5:23 PM
To: Towertalk
Subject: [TowerTalk] HFTA first impressions


Just got my new ARRL Antenna book, which I bought primarily for the copy
of HFTA.  Here are my first impressions..

1) Why must they provide nagware copies of software that have time
limits? I understand and support the concept of shareware, but, on the
other hand, it would have been nice if the ARRL blurb said: "limited
functionality versions of popular programs".  I wouldn't even mind
getting developmental, beta type software on the disk, providing it was
disclosed up front.

2) The instructions on getting DEM data are mindbendingly complex and
confusing, especially with respect to properly installing it in the
right directories, etc.  The microDEM program is quite slick (probably
too powerful for this application, by the way), but all that capability
means it takes a lot of configuring.  A program like RadioMobile does
this MUCH better.

3) The instructions given for creating the terrain profile files do not
work.  The version of MicroDEM on the CDROM doesn't save the profiles
created in the viewshed analysis. It doesn't allow you to click the
"save radials" option, which is grayed out.  The HFTA pdf file tells you
that you can enter the lat/lon for the viewpoint once you have clicked
on the DEM data, but in reality, it's where the cursor is when you
(double) click that determines the viewpoint.

4) It would have been much better if they had simply provided a single
program that you enter the lat/lon of the station, how many radials, how
far, what post spacing, etc. in a dialog, and it would spit out the
required text files.  Sure, it's cool to use a sophisticated mapping
program, but there's a lot more that can go wrong.

5) There is no documentation about how HFTA works, in either the program
documentation, or in the Antenna Book.  There's a general description in
the book of the diffraction analysis, but no theory, and what's
important, no place to go look for a better description.  The textbook
cited on GTD is all well and good, but I wasn't looking forward to
rederiving how HFTA might work from first principles.

For any sort of modeling program, it's important that the theory be
described somewhere, or it's impossible to validate the program.  Say
you get some sort of output from HFTA... how would you verify that
independently?  For a program such as this, where the development budget
is presumably quite small (they're giving it away essentially for free,
after all), the value of legions of unpaid testers and validators would
be significant.  (The book mentions the work of Breakall, et al and
their modified version of NEC-BSC that they did field tests on, but
doesn't say whether HFTA actually uses the algorithms developed for that
work.  The IEEE A&P paper is fairly vague on the details of the
implementation)  One reason NEC is still popular after all these years
is that there is copious documentation on how it works.

6) there are a number of fairly obvious formatting errors in the dialogs
(Options dialog, where the caption text on the command button doesn't
fit and isn't readable).  Such things don't fill one with confidence
about the testing and validation process.

7) No documentation about how the "figure of merit" is calculated in
HFTA

8) It's not clear what antenna pattern is being modeled in HFTA.  The
book makes a mention of a cosine squared pattern for the default 4 el
beam, but what's the pattern for the others?  Is it a cos^N type
pattern? In particular, what's the vertical pattern assumed.

Overall, a good start, but kind of a clunky distribution/installation
mechanism, and there needs to be some more documentation provided,
somewhere.

Jim Lux, W6RMK




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