[Elecraft] Sloping Terrain vs Feedline Losses

[Jim Brown]

On Wed,7/13/2016 10:29 AM, David Gilbert wrote:
> I have no idea how or to what extent terrain affects a vertically 
> polarized signal.  I am, however, pretty certain that if it does at 
> all it would be worth more than 1 db.

N6BT presented excellent experimental work on the effect of terrain on 
vertically polarized antennas as his contribution to the Pacificon 
Antenna forum last fall. He's been working on vertical dipoles for 
several years now. This experiment included setting one up at various 
locations on a broad knoll with drop-offs in most directions. He made 
some measurements of vertical pattern using a drone, and also used the 
antennas at those various locations to make contacts on the air.  As I 
recall, he was operating on 20M, but I could be wrong about that.

The antenna location near a dropoff in the direction of SA yielded QSOs 
with SA, but none with JA. A location near a dropoff in the direction of 
JA yielded JA QSOs but no SA. And a setup in the center of the knoll, 
relatively far from the dropoffs yielded no QSOs with SA or JA. And his 
measurements with the drone showed vertical radiation increasing below 0 
degrees in the direction of the dropoff.

> I've always wished we had a version of HFTA that handled vertically 
> polarized antennas ... that would probably be enlightening.  I've also 
> tried on occasion to use EZNEC+ for the same purpose since it allows 
> you to specify at least two different zones around the antenna, but I 
> didn't have much success with that.

The interaction of vertically and horizontally polarized signals with 
ground is quite different, so the math is quite different. Among other 
things, a primary determinant of ground interaction with vertical 
antennas is soil conductivity in the far field (that is, at the point of 
interaction). Height is also a factor. With horizontal antennas, soil 
conductivity is essentially insignificant, and the primary determinants 
are height and the elevation profile.

>
> I'm one of those who had quite good luck with roof mounted verticals, 
> but it's hard to say whether any improvement (if there was one) was 
> the result of distance from lossy ground or simply the ability to 
> shoot over lossy surrounding structures like trees and houses.

See my NEC study on this, which is in line with your observations. When 
I presented this material to an NCCC meeting a few years ago, the OT 
hams with solid engineering background were nodding their heads in 
agreement.

http://k9yc.com/AntennaPlanning.pdf
http://k9yc.com/VerticalHeight.pdf

> I do think it is more than "folklore" that elevated radials have 
> benefits over in-ground radials unless the in-ground radial system is 
> reasonably extensive.  There have been some pretty decent studies on 
> that.

Yep. N6LF has done lots of excellent work, which is on his website.

http://www.antennasbyn6lf.com/

I've used part of his work in my applications note/tutorial on antennas 
for 160M.

http://k9yc.com/160MPacificon.pdf

73, Jim K9YC