Oddity of ground mounted antenna's.
 

Hi Gang

I recently moved from a fairly flat state to one that is mountainous.

In getting to know the local area hams I have visited quite a few this
past year.

Several of them have their ground mounted HF antenna's perpendicular
to the grade of the land rather than vertical. In other words, the
top of the antenna is roughly 90 inches off center toward the downhill
side.

The only reasoning I have received thus far is it works better that
way here. But not everyone adheres to doing it that way, all
commercial antenna's are vertical.

What Gives?

TTUL
Gary

On 02 Dec 2004 11:51:12 EST, am (Gary V.
Deutschmann, Sr.) wrote:
What Gives?

Hi Gary,

Do they have the faith to build their walls that way too? Look at the
horizontals. Do they ridge run, or do they follow the down hill slope
too?

The better question is: How much better is theirs than their
neighbor's vertical (as opposed to their perpendicular)?

The best question is: How do they know?

Kinda reminds me of the Katherine Hepburn movie "Bringing Up Baby"
where she breaks one heel of her high heels and starts loping along:
"I feel like I was born on the side of a hill."

73's
Richard Clark, KB7QHC

Hello Gary,

Don't know from personal experience, but Les Moxon, author of HF
Antennas for all Locations, seems to believe it creates an advantage.
You might want to read his thoughts on that.

Good luck.

Chuck

There's a breed of Algerian goats with legs on one side longer than the
other.

They live on the sides of steep mountains.

Since NEC cannot model a sloping ground, just try modeling a leaning
vertical, and see how it effects the pattern. I seriously doubt there would
be much difference. Certainly nothing you would notice.

Frank


"Richard Clark" wrote in message
...
On 02 Dec 2004 11:51:12 EST, am (Gary V.
Deutschmann, Sr.) wrote:
What Gives?

Hi Gary,

Do they have the faith to build their walls that way too? Look at the
horizontals. Do they ridge run, or do they follow the down hill slope
too?

The better question is: How much better is theirs than their
neighbor's vertical (as opposed to their perpendicular)?

The best question is: How do they know?

Kinda reminds me of the Katherine Hepburn movie "Bringing Up Baby"
where she breaks one heel of her high heels and starts loping along:
"I feel like I was born on the side of a hill."

73's
Richard Clark, KB7QHC

Reg Edwards wrote:
There's a breed of Algerian goats with legs on one side longer than the
other.

....and to go back the way they came, they must walk backwards?


They live on the sides of steep mountains.


Cheers - LH

Reg Edwards wrote:
There's a breed of Algerian goats with legs on one side longer than the
other.

....and to go back the way they came, they must walk backwards?


They live on the sides of steep mountains.


Cheers - LH

This can easily be done with the free EZNEC demo program available from
http://eznec.com. Here's a step-by-step for the demo or any other EZNEC
v. 4.0 program:

1. Open example file Vert1.EZ. (Click the Open button, enter Vert1, then
click Open in the file selection window.)
2. Click FF Plot to generate a 2D elevation plot of the vertical antenna.
3. In the 2D Plot Window, open the File menu, select Save Trace As,
enter a name in the blank box, and click Save. You can close the 2D Plot
Window to get it out of the way.
4. Click the View Ant button so you can see what you're doing.
5. Click on the Wires line in the large white window to open the Wires
Window.
6. In the Wires Window, open the Wires menu and select Rotate Wires.
(This feature isn't available in EZNEC v. 3.0 or earlier versions.)
7. In the Rotate Wires dialog box, make the following changes:
Rotation Amount: Enter the angle of the ground slope, and change the
direction to CW (to simulate ground sloping down to
the right)
Rotation Axis: Y
Then click Ok. You'll now see the tilted antenna. (The rotation will
seem to be CCW, but that's because we're looking at the Y axis in the
minus direction.)
8. Click FF Plot to generate a 2D plot.
9. In the 2D Plot window, open the File menu and select Add Trace. Enter
the name of the plot of the vertical you saved earlier and click Open.
You'll now see the plots of the vertical and tilted antenna superimposed.
10. If you'd like to see the dB difference between plots at any
elevation angle, click the name of the recalled trace near the upper
left corner of the plot window. The cursor will jump to the recalled
trace, and the difference in dB appears as the bottom line of the right
column in the data window below the plot. (This feature isn't available
in EZNEC v. 3.0 or earlier versions.) If you don't see the data window,
open the View menu and click Show Data. You can move the cursor by
dragging it with the mouse, or with the arrow keys.
11. To see what the patterns would look like when the ground is tilted,
print the plot (File/Print Plot), then rotate it clockwise by the angle
of the ground tilt. Note that this assumes that the ground is flat and
continues forever at the tilt angle, which of course can't be true. But
it'll give you a good general idea of the effect of tilting the antenna.

If you get confused about how the plot is oriented relative to the
antenna, go to the View Antenna display. Open the View menu, select
Objects, then check the 2D Pattern box. This will superimpose a
correctly oriented 2D pattern on the drawing of the antenna.

I did the experiment using a 30 degree tilt, and found a difference of
1.31 dB at an indicated elevation angle of 30 degrees. That would be at
the horizon, taking into account the ground tilt. At an indicated
elevation angle of 40 degrees (10 degrees above the horizon when ground
tilt is considered), the difference is 1.77 dB. You can modify the
ground conductivity and permittivity and repeat the experiment to see
how this changes with different ground types.

Roy Lewallen, W7EL

Frank wrote:

Since NEC cannot model a sloping ground, just try modeling a leaning
vertical, and see how it effects the pattern. I seriously doubt there would
be much difference. Certainly nothing you would notice.

Frank

On Thu, 02 Dec 2004 13:45:35 -0800, Roy Lewallen
wrote:

I did the experiment using a 30 degree tilt, and found a difference of
1.31 dB at an indicated elevation angle of 30 degrees. That would be at
the horizon, taking into account the ground tilt.

Hi All,

This is a pretty radical slope. The one I lived on was closer to
20-25 degrees and it was (with low brush) a bear to climb (and to fall
without holding a rope for balance). When I do the trig for 30
degrees and stand with my feet one foot apart, shoulders and hips
aligned with the slope, that leaves one foot 7 inches higher than the
other. That's gonna take some stilleto heels. ;-)

That aside for the heartier cragsmen, this also presumes (from EZNEC's
propensity for a flat earth far field model) that the slope is infinte
(or a pretty tall hill indeed). Gee, on that hill everything must be
line of sight anyway! Who needs skip?

But then, no one lives in the valley. :-(

73's
Richard Clark, KB7QHC

Reg Edwards wrote:
There's a breed of Algerian goats with legs on one side longer than the
other.

...and to go back the way they came, they must walk backwards?

Cheers - LH

========================================

No! They just keep walking in the same direction. They have inherited a
gene for sensing contour lines, never failing to get to where they want to
be.

Hannibal, around 219BC, being unaware of genes in those ancient days,
considered mountain goats could be useful on the famous crossing of the
Swiss Alps on his way to Rome. But on second thoughts he decided to use
elephants who, as you know, walk trunk-to-tail. Neither he nor the
elephants quite made it to Rome.
---
Reg