Tried to make the subject grab a bit.

I just fininshed the ARRL Antenna Book Chapter on Effects of Ground.
There are HFTA graphs showing elevation response for various antenna
configurations (mostly Yagis).

Most arrays show good response up to 12 degrees above the horizon, then
many show a null and then, a second peak around 25 to 30 degrees above
the horizon.

Here's my question:
At 25 to 30 degrees elevation response, aren't these waves leaving the
ionosphere (i.e., refracted instead of reflected)?

Am I right to consider this component of propagation to have left the earth?

This would indicate a substantial fraction of each amateur transmission
is sent into space.

I always thought Broadcast transmissions were most likely to emanate
from Earth. Are hams more or less likely to transmit into space than
Broadcast?

John
(who wishes to remain a student and never an expert)

On Sat, 01 Jul 2006 11:09:22 -0400, jawod wrote:

Here's my question:
At 25 to 30 degrees elevation response, aren't these waves leaving the
ionosphere (i.e., refracted instead of reflected)?

In your HFTA program run the antennas at various heights. Amongst
other things,varying the height of the antenna will change the
elevation angle of the lobes.

Danny, K6MHE

On Sat, 01 Jul 2006 11:09:22 -0400, jawod wrote:
Here's my question:
At 25 to 30 degrees elevation response, aren't these waves leaving the
ionosphere (i.e., refracted instead of reflected)?

Hi John,

You are confusing models of propagation with models for antenna lobe
characteristics. The lobes certainly have a major impact on
propagation, but the antenna modeler is not concerned with that. The
terrain modeler is not a propagation modeler. For that, consult
VOACAP or WINCAP. They are properly concerned with ionospheric
issues, but they are also driven by antenna models too.

Am I right to consider this component of propagation to have left the earth?

To some degree, yes, but it has very little bearing on what you are
focused on here.

This would indicate a substantial fraction of each amateur transmission
is sent into space.

In fact, no. The apportionment of the energy into lobes is simply
robbing Peter to pay Paul. The nulls were developed from energy lost
to the peaked lobes. This is very loose analogy because energy was
never lost, it is merely the combination from many sources that makes
this lobe shape appears as it does.

An antenna radiates from every portion of its structure and in every
direction. When all contributions are viewed from a distance, some
portions of the structure are out of phase with respect to others
portions. When those two contributions are 180° out of phase, that
remote point at where they combine perceives a null (a destructive
combination). At some other remote point, those same two
contributions may combine constructively for a peak response. Same
energies all around, but path lengths shift the wave phases and how
they combine constructs the characteristic lobe shape.

If you took college physics, you must have seen how two charges
separated by a distance combine their effects at remote points to
offer an "electric dipole." Same logic.

73's
Richard Clark, KB7QHC

Whether you call it Refraction or Reflection hardly matters.

What matters is that the wave, in effect, is reflected from an
ionospheric layer at at a particular height, roughly according to
optical laws. Trigonometry Rules!

Since the transmitted 'beam' has a very wide angle in the vertical
plane, the energy returns to earth over an even wider range of
distances.

The 'elevation angle' reported by antenna simulation programs is not
very meaningfull. It contains very little useful information, mainly
because the height of a reflecting layer is unknown at the time of
transmission. Neither is the number of hops known to a particular
destination.
----
Reg.

Hi Richard,

It's good to see you are NOT using Queen Elizabeth the First's,
Shakespear's poetical, but somewhat difficult to understand language.
Inapropriate for technical matters.

There must be other newsgroups available to people who enjoy writing
sonnets.

As we always knew by reading, with difficulty, between the lines, you
are an exceptionally knowledgeable person. Please keep up the good
work by continuing to use modern American English, as demonstrated in
your last valuable contribution. Thank you.
----
Yours, Punchinello

On Sat, 1 Jul 2006 18:15:01 +0100, "Reg Edwards"
wrote:

It's good to see you are NOT using Queen Elizabeth the First's,
Shakespear's poetical, but somewhat difficult to understand language.

Hi Reggie,

I reserve that for the technical Falstaffs.

Inapropriate for technical matters.

Their usual plea is
"discretion is the better part of a direct answer...."

As such, technical matters are notably absent, or at best serving as a
stalking horse. For those who are shy in their English skills,
"stalking horse" finds its current usage in "trolling."

73's
Richard Clark, KB7QHC

Richard,

I have NEVER considered your contributions to be deliberate trolling.

You just can't help mixing up your desire to produce poetry with your
desite to spread technical enlightonment. The two don't mix very well.

I am 3/4 of the way down a bottle of "Cotes du Rhone Villages" red,
2004, 14.5% by volume. (I have a great liking for our near
neighbours, the French.) So please excuse me if my psycho-analysis is
not exactly as you might perceive it yourself.
----
Yours, Punchinello.

"jawod" wrote in message
...
Tried to make the subject grab a bit.

I just fininshed the ARRL Antenna Book Chapter on Effects of Ground. There
are HFTA graphs showing elevation response for various antenna
configurations (mostly Yagis).

Most arrays show good response up to 12 degrees above the horizon, then
many show a null and then, a second peak around 25 to 30 degrees above the
horizon.

that is a function of height. the main lobe from the antenna is aimed at
the horizon and there are other lobes from the design of then antenna. then
reflections from the ground cause more vertical variations. these are
dependent on the height and the terrain around the antenna.


Here's my question:
At 25 to 30 degrees elevation response, aren't these waves leaving the
ionosphere (i.e., refracted instead of reflected)?

not necessarily. look at the arrival angle statistics and you will see that
frequently very high angle propagation is possible. usually higher angles
mean shorter distances but at times you can get many short high angle hops
to cover long distances also.


Am I right to consider this component of propagation to have left the
earth?

This would indicate a substantial fraction of each amateur transmission
is sent into space.

I always thought Broadcast transmissions were most likely to emanate from
Earth. Are hams more or less likely to transmit into space than
Broadcast?

broadcast is more likely. there are many more broadcast stations on the air
24x7, over the same range of spectrum that we use, and running much higher
power than we use. the most likely signals to reach out from earth are
likely fm broadcast and tv signals since those are normally well above the
critical frequency that reflects from the ionosphere and can be fairly high
power. lower hf, mf, and lf are less likely to get out as they reflect from
the ionosphere even at very high angles.



John
(who wishes to remain a student and never an expert)

Dear John:
If you were a radio amateur who is interested in working other radio
amateurs at a great distance, then you wish to have a significant portion of
your antenna's radiation within about 12 to 2 degrees above the horizon.

In tern, this goal suggests that a preferred height for an HF,
horizontally-polarized antenna is between 2 and 2.5 wavelengths above
ground.

If the higher angle radiation does not pass through the ionosphere, it
contributes to interference to (relatively) nearby stations (and, because
the antenna probably is used for reception, contributes to hearing nearby
stations). Expensive HF antenna systems exist that significantly suppress
all except the lowest lobe.

If you wish to be a student of antennas, do invest in Kraus' 3rd edition
of Antennas. Read and study the book starting with the first chapter.

Regards, Mac N8TT


--
J. Mc Laughlin; Michigan U.S.A.
Home:
"jawod" wrote in message
...
Tried to make the subject grab a bit.

I just fininshed the ARRL Antenna Book Chapter on Effects of Ground.
There are HFTA graphs showing elevation response for various antenna
configurations (mostly Yagis).

Most arrays show good response up to 12 degrees above the horizon, then
many show a null and then, a second peak around 25 to 30 degrees above
the horizon.

Here's my question:
At 25 to 30 degrees elevation response, aren't these waves leaving the
ionosphere (i.e., refracted instead of reflected)?

Am I right to consider this component of propagation to have left the
earth?

This would indicate a substantial fraction of each amateur transmission
is sent into space.

I always thought Broadcast transmissions were most likely to emanate
from Earth. Are hams more or less likely to transmit into space than
Broadcast?

John
(who wishes to remain a student and never an expert)

On Sat, 1 Jul 2006 19:50:43 +0100, "Reg Edwards"
wrote:

I am 3/4 of the way down a bottle of "Cotes du Rhone Villages" red,

I've seen a varietal called "Goats do Roam"

2004, 14.5% by volume.

YOW!

(I have a great liking for our near neighbours, the French.)

An empty bottle of Quadrupel "Three Philosophers" Belgian lambic ale
(9.8%) sits nearby.

So please excuse me if my psycho-analysis is
not exactly as you might perceive it yourself.

No, our both having included quantifiables from bench testing allows
us to add to the topic.

73's
Richard Clark, KB7QHC