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Old June 21st 09, 03:59 AM posted to rec.radio.amateur.antenna
tom tom is offline
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Default Horizontal Dipole - zero degrees elevation

Frank wrote:
At 10,000 meters, 3 meters off the ground:
E(theta) is maximum off the ends at 3.5E-8 V/m
E(phi) is maximum off the sides at 2.6E-7 V/m

This agrees with the expected horizontal polarization off
the sides, and vertical polarization off the ends.

Frank, VE6CB

Now what's the result without the surface wave?

Roy Lewallen, W7EL


Good point: E(theta) off the ends 1.25E-7 V/m
E(phi) off the sides 1.04E-7 V/m

Frank



Ok, how do I get those, and select those, results? I looked for it, but
couldn't find it in EZNEC.

tom
K0TAR
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Old June 21st 09, 04:08 AM posted to rec.radio.amateur.antenna
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Default Horizontal Dipole - zero degrees elevation


"tom" wrote in message
. net...
Frank wrote:
At 10,000 meters, 3 meters off the ground:
E(theta) is maximum off the ends at 3.5E-8 V/m
E(phi) is maximum off the sides at 2.6E-7 V/m

This agrees with the expected horizontal polarization off
the sides, and vertical polarization off the ends.

Frank, VE6CB
Now what's the result without the surface wave?

Roy Lewallen, W7EL


Good point: E(theta) off the ends 1.25E-7 V/m
E(phi) off the sides 1.04E-7 V/m

Frank


Ok, how do I get those, and select those, results? I looked for it, but
couldn't find it in EZNEC.

tom
K0TAR


It comes from the "RP" card; line 8 below. I do not know how to
implement this line of code in EZNEC. I am sure there are
plenty of people In this group that know how to do it.

Frank
VE6CB

CM Horizontal Dipole
CE
GW 1 11 0 0 3 0 1.5 3 0.01
GE 1 -1 0
GN 2 0 0 0 13.0000 0.0050
FR 0 1 0 0 100 1
EX 0 1 6 0 1 0
RP 1 1 360 0000 3 0 1.00000 1.00000 10000
EN


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Old June 21st 09, 07:19 AM posted to rec.radio.amateur.antenna
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Default Horizontal Dipole - zero degrees elevation

On Sat, 20 Jun 2009 20:50:59 -0400, wrote:

So,EZNEC models "very far away" and, in my example, the channel 23
tower is 5.1 miles away (about 10,000 wavelengths) so I need a
different model? A different program? I think you are correct in
saying that is my main confusion.


Hi Pat,

You can use the "near field" table to then build a second antenna
(representing your own at the proper distance) with a load, and then
look at the power developed to that load to see how things perform.
This goes beyond the normal use, but for those who will slog through
it, there's a way.

Here, even if you can "see" the Channel 23 transmitting antenna, then
its various reflections could add up to ZERO. This, again, confounds
expectation, but it is the experience of every mobile operator who
encounters "picket fencing."

Good example. I started in this hobby 41 years ago on 6 meter AM.
However, I always thought that picket fencing was caused by
reflections from various objects (power lines, airplanes, metal
fences, water towers, etc,etc) rather than the radiation patterns of
the antennas.


A combination of both, naturally.

Since my last post, I changed the polarization of my EZNEC dipole to
virtical. I expected a nice donut shaped pattern, but instead saw
another flower shaped pattern with deep nulls at various elevations
including zero degrees. When I select free space, I get the donut.


This is the contribution of ground reflections (which occurs for the
horizontal as well).

I truely believe EZNEC gives valid results when provided with a proper
model. So, either I am not providing a good model to EZNEC (likely)


It takes discipline to look at the situation without the filter of
expectation driving you.

or a simple virtical dipole radiates very little at zero degrees
(-90dBi) and a lot at one degree (7.33 dBi), etc, etc (which seems
less likely to me).


You now enter into the realm of the "Brewster Angle." This is a
phenomenon specific to vertical polarization (originally from the
field of optics) when an incident ray of radiation meets an interface
and is wholly absorbed by the second media (earth in our case) without
any reflection possible, but only for a "critical angle" (another name
for this) or less. If you were to change the characteristic of the
earth's conductivity (accessible in EZNEC), then you would find you
can shift that angle. Selecting a "perfect" ground will present you
with a total absence of the Brewster effect, and as high a zero angle
response as you might ever want to see.

73's
Richard Clark, KB7QHC
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Old June 21st 09, 07:03 PM posted to rec.radio.amateur.antenna
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Default Horizontal Dipole - zero degrees elevation

On Sun, 21 Jun 2009 06:19:02 -0400, wrote:

Thanks again, Richard. I just purchased an EZNEC license so I will
try that to further my learning. (I had been using the demo version).


Have fun, Pat.

73's
Richard Clark, KB7QHC
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