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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