[TowerTalk] 160 meter vertical on sloping ground

Wed Jan 15 16:51:14 EST 2025

Brian, the photos you mention of K6STI, W7EL and WA3FET at W6NL are on 
slide 27 of my 2007 Dayton talk at 
https://www.kkn.net/dayton2007/w6nl_ant.pdf Dean, N6BV, wasn't able to 
be there, but we all corresponded a lot about the need for PC terrain 
software.

An interesting reference on this specific subject is L. B. Cebik, W4RNL, 
“Verticals At and Over Ground, Sensible Expectations,” 
http://www.antentop.org/w4rnl.001/amod12.html

But watch out! My grandkids accuse me (correctly) of TMI.

The subject of the effect of foreground slope goes way back. The first 
reference I've found is the 1932 paper, R. K. Potter & H. T. Friis, 
“Some Effects of Topography and Ground on Short-wave Reception,” Proc. 
IRE, Vol 20, No. 4, April 1932, see the graphs of "tipped elevation 
pattern," pp. 712 & 713, https://ieeexplore.ieee.org/document/1685112

The works of Fred Terman include detailed information about the 
reflection of both horizontally and vertically polarized radio waves, 
leading to the 1955 edition of his "Electronic and Radio Engineering."

I got focused on the favorable effect of our foreground slope after 
Willy, UA9BA, asked me in a late-1970s QSO, "“How come I only hear you?” 
I was led to P. D. Rockwell, W3AFM. "Station Design for QX, Part I — 
Antenna Topics and Siting, QST, Sept. 1966, see 
https://www.rfcafe.com/references/qst/station-design-dx-september-1966-qst.htm

A pioneering view of the impact of foreground slope is, of course, due 
to Les Moxon, G6XN, who described what came to be called "Moxon Slopes" 
in L. A Moxon, G6XN, "HF Antennas for All Locations," RSGB, 1982. Visits 
with Les at his UK home and here were an inspiration.

I learned about the work of George Hagn at SRI that included mainframe 
3D modeling, described in G. Hagn, "HF Receiving Antenna Directivity 
Patterns and Gain for lonospheric Propagation Model Predictions for 
Short-Wave Broadcasting," IEEE Trans on Broadcasting, June, 1988, 
https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1439

I referenced these in my 1992 book, which I was encouraged to write by 
G6XN, W6SAI and others (see photo of us at slide 14 of my 2007 Dayton 
talk noted above), "Physical Design of Yagi Antennas," see Ch. 1, 1.8 
Siting of Yagi Antennas over Sloping Foreground, and Ch. 10, 10.1 Ground 
Reflection an Antenna Performance & 10.2 Avoiding Foreground Shadowing, 
https://www.dropbox.com/scl/fi/j7kkt63nyyh2pag0g9avj/Physical-Design-Of-Yagi-Antennas-D-B-Leeson-V2.pdf

That led me to discussions with Jim Breakall, WA3FET, Dean Straw, N6BV. 
Roy Lewallen, W7EL and Brian Beezely, K6STI. See J.K. Breakall; J.S. 
Young; G.H. Hagn; R.W. Adler; D.L. Faust; D.H. Werner, "The modeling and 
measurement of HF antenna skywave radiation patterns in irregular 
terrain," IEEE Transactions on Antennas, Volume 42, Issue 7, July 1994, 
https://ieeexplore.ieee.org/document/299595

R. Dean Straw, N6BV, "The Effect of Local Terrain on HF Launch Angles", 
QEX, July 1995, 
https://archive.org/stream/QEX19812016/QEX%201995/QEX%201995-07_djvu.txt

Since then, the development of HFTA, TA, EZNEC and 4NEC2, along with 
MMANA-GAL, NEC-Win and others, have given a new level of insight, using 
the benefit of personal computing. In order to fit the available 
capability, these are 2D, but extremely useful. This is covered in the 
recent ARRL Antenna Handbooks, as well as the online work of L. B. 
Cebik, W4RNL, see his "Antenna Modeling Programs," 
https://www.antenna2.net/cebik/content/model/nec.html.

For discussions of ground reflection and foreground slopes, see these:

Dean Straw, N6BV, "Selected Terrain Studies for Optimum HF Station 
Performance," 2004, Dayton Antenna Forum, 
https://www.kkn.net/dayton2004/N6BV-Dayton-2004.pdf

R. Dean Straw, N6BV, "Another Way to View Propagation Predictions for 
DXing and Contesting," Friday, 2006, Dayton Antenna Forum, 
https://www.kkn.net/dayton2006/N6BV-Dayton-2006.pdf

D. Leeson, W6NL, "Antenna Topics," Dayton 2007, see photos slides 14 & 
27, https://www.kkn.net/dayton2007/w6nl_ant.pdf

D. Leeson, W6NL, "Ideas for More Effective HF Antennas: Geography, 
Terrain, Siting and Operation," Dayton 2009, 
https://www.kkn.net/dayton2009/w6nl_2009.pdf

D. Leeson, W6NL, "Match HF Antennas to the Ionosphere & Terrain," 
https://www.dropbox.com/s/hhc00iy6t4h509c/Ionospheric%20Radio%20REDXA_sm.pdf?dl=0

J. Breakall, WA3FET, "Maximizing Performance of HF Antennas with 
Irregular Terrain," 2021, Contest University, 
www.contestuniversity.com/wp-content/uploads/2021/01/Contest-University-HF-Propagation-in-Irregular-Terrain.pdf

The work of K6STI, N6BV, WA3FET, W7EL and others has added tremendously 
to our understanding of foreground reflection and how to use it. The 
specific study of vertical antennas over sloping foreground has a lot of 
room to grow, and it will be interesting to see the results.

So TMI proved! It's a big subject, there's so much more, but enough...

73 de Dave, W6NL/HC8L

On 1/15/25 10:51 AM, Brian Beezley wrote:
> "Today, with DEMs available to generate the "tiles" for a full 3d
> model would be straightforward. That was one of the challenges when
> Breakall did his work."
> 
> 
> Jim, the data I would need are measured 3D patterns to validate a 3D
>  modeling program. I thought a drone might generate them, now I don't
>  think so. There are many sources of error with a drone, some rather
>  subtle. It might work in certain limited terrain, but not in
> general. There's no way one would work at my QTH.
> 
> 
> "I'm not sure an ever increasing model fidelity is useful."
> 
> 
> The issue with a radial-only model is that it can be entirely wrong,
> not just off a bit. Worse, it gives no indication that the result is
>  unreliable. I think it's possible to use a radial-only model under 
> certain circumstances, but you need to carefully vet the terrain. It
>  definitely wouldn't work in most directions at my QTH. And while
> some directions look benign, I'm not sure they really are. It's
> tricky!
> 
> 
> "My understanding is that HFTA is horizontal pol only (the reflection
>  model is simpler)."
> 
> 
> I don't know what HFTA does, but TA used specified ground constants
> with Fresnel reflection coefficients for both horizontal and vertical
>  polarization at all reflection points. Vertical is no more difficult
>  than horizontal. The equations are just a little different.
> 
> Incidentally, after months of making innumerable errors of all kinds,
> I think I finally have an accurate stratified ground model. Its 
> application is rather limited, as is the available stratified ground
>  data. But it provides some insight into the accuracy of surface
> ground probes:
> 
> http://ham-radio.com/k6sti/sg.htm
> 
> My writeup on the Hagn generic curves, which yield ground constants
> much more appropriate at HF than the figures antenna analysis
> programs suggest, is here:
> 
> http://ham-radio.com/k6sti/hfgc.htm
> 
> Brian
> 
> _______________________________________________
> 
> 
> 
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