|To:||"Jim Lux" <firstname.lastname@example.org>,"Towertalk" <email@example.com>|
|Subject:||Re: [TowerTalk] HFTA first impressions|
|From:||Pete Smith <firstname.lastname@example.org>|
|Date:||Sun, 09 Nov 2003 20:57:43 -0500|
At 05:22 PM 11/9/03 -0800, Jim Lux wrote:|
Just got my new ARRL Antenna book, which I bought primarily for the copy of HFTA. Here are my first impressions..
? I hope Dean will respond to this. Why should it be time-limited since there's no shareware charge involved.
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.
Never heard of it -- I worked with Dean on developing the use of MicroDEM, which was originally proposed by Kevan Nason, NS4T. During development of HFTA, the USGS seam;less server came out, which offered a nicer solution to the problem of getting DEM data specific to a particular site. Sgain, I've never heard of RadioMobile, but suggest you tell Dean about it if it's a better way. MicroDEM is a very complex program developed entirely for another purpose, but its developer has been very helpful in developing its use with HFTA.
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.
Not if you have set up the microDEM defaults properly. It is easy to skip over that point. But if you take it step by step it works fine.
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.
But compare this to sitting down with a topo map, a ruler, and a pencil. MicroDEM was out there, and it works. The development effort for a separate program such as you describe would have been prohibitive.
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.
This I can speak to, because the FOM is based on a piece I published in the September-October 2000 NCJ, titled "Scoring Your Antenna System." Essentially, the pattern of the antenna is converted to power ratios, and then the power at each elevation angle is multiplied times the percentage of the time that angle is active to a given target area. The resultant weighted average is then converted back to dB. I agree that it would have been helpful if the Antenna Book had cited that article and the correction provided by Bruce Horn, WA7BNM, which was published in NCJ 6 months or so later.
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.
I think the documentation states that the antennas are assumed to be point sources. For this reason, neither HFTA nor TA give reliable results in some extreme cases, such as very closely space stacks. There is also some uncertainty about the results at very low take-off angles, where the terrain profile is highly detailed. I defer to Dean on the cause and potential solutions.
73, Pete N4ZR The World HF Contest Station Database was updated October 29. 2469 stations are listed -- 29 new and over 100 updated. Are you current? www.pvrc.org/wcsd/wcsdsearch.htm
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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