HFTA-ARRL-Space
 

Richard Clark wrote:
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
Thanks for setting me right!

John
AB8WH

HFTA-ARRL-Space
 

Richard Clark wrote:
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,
snip
2004, 14.5% by volume.

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

snip
73's
Richard Clark, KB7QHC

While we're at it, I am just enjoying my first ever 20th Aniversary
Summit Brewing Extra Special Bitter Ale. Just out this weekend. No
%age listed. And not too bitter first taste, very smooth, light after
bitter on the back of the tongue. Summit made another hit.

tom
K0TAR

HFTA-ARRL-Space
 

Reg Edwards wrote:
Whether you call it Refraction or Reflection hardly matters.

This I don't understand. To me, refraction versus reflection IS the
issue. In optics, Brewster's angle is used. I still don't quite
understand thte PseudoBrewster's Angle...it seems to have a different
definition (at least in the ARRL book).

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.



Reg,
Thanks for your answer.

I guess I was trying to get at how much ham radio is propagated into
space. Certainly SOME does.

How does this compare to that amount propagated into space by Broadcast?

My assumption has been that VHF TV, etc is easily passed through the
ionosphere (minimally refracted).

HFTA-ARRL-Space
 

Dave wrote:


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.


Radar is the best we do, but not much information is transmitted beyond
the fact that we are here, the beam is usually narrow, and the direction
varies quickly. EME is a distant 2nd, carries real information in
simple codes, the direction varies slowly, the beamwidth is usually low
(on high GHz bands it can be less than the width of the moon), and the
number of transmitters is very low.

Either one of the previous could be picked up from a fair distance, but
not likely because of the narrow angles and varying direction. And
commercial broadcasting doesn't have the ERP in any particular direction
to carry far. We live next to a very large noise source that would tend
to swamp out what we generate.

tom
K0TAR

HFTA-ARRL-Space
 

Dave wrote:
"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)



Thanks to all for the "enlightenment".

Guess I've got a little SETI streak in me. I just got back a copy of an
Astrobiology text that I borrowed out. It's by Gilmour and Sephton,
Cambridge University Press if anyone's interested.

John

HFTA-ARRL-Space
 

Tom Ring wrote:

Radar is the best we do, but not much information is transmitted beyond
the fact that we are here, the beam is usually narrow, and the direction
varies quickly. EME is a distant 2nd, carries real information in
simple codes, the direction varies slowly, the beamwidth is usually low
(on high GHz bands it can be less than the width of the moon), and the
number of transmitters is very low.

Either one of the previous could be picked up from a fair distance, but
not likely because of the narrow angles and varying direction. And
commercial broadcasting doesn't have the ERP in any particular direction
to carry far. We live next to a very large noise source that would tend
to swamp out what we generate.

VHF and UHF emissions escalated rapidly after WWII with the
popularization of TV, and these readily penetrate the ionosphere. So
there's a sphere of such emissions radiating outward from the Earth at
the speed of light. And at the leading edge of this radiation sphere are
the McCarthy hearings and the Howdy Doody show. No wonder the ETs have
left us alone!

Roy Lewallen, W7EL

HFTA-ARRL-Space
 

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

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)


To: "Richard Clark"
Subject: Please Post in rraa
From: "Walter Maxwell"
Date: Sat, 1 Jul 2006 17:31:29 -0400

Richard, I've been trying to post the msg below to the HFTA-ARRL-Space
thread, but after three attempts to send it it doesn't get posted.
Would you please post it for me in the spot following Mac's?

Walt, W2DU

Hello John,

I believe your other respondents missed one of your points concerning
reflection and refraction, and therefore didn't respond completely to
it.

Whether reflection, refraction, or total penetration of the ionosphere
occurs depends on the ionospheric layer, the time of day that
determines the sun angle on the layer, the resulting level of
ionization, the angle the ray makes on incidence with the layer, and
the frequency of the energy in the arriving ray.

Consequently, the answer is complex. As we know, when the frequency is
high enough (VHF and above) the result is total penetration--no
reflection or refraction--line of sight reception only.

On the other hand, at HF the ratio between reflection and refraction
varies. There are times when both occur. During those times the
portion of the incident ray that is reflected returns to earth, while
the portion that is refracted continues on through the ionosphere into
space and never returns. I'm not sufficiently knowledgeable on the
subject to go into further detail, but now that they've been nudged,
either Richard C or Reggie can. Or someone else more knowledgeable
than I.

Walt, W2DU

HFTA-ARRL-Space
 

Roy Lewallen wrote:

VHF and UHF emissions escalated rapidly after WWII with the
popularization of TV, and these readily penetrate the ionosphere. So
there's a sphere of such emissions radiating outward from the Earth at
the speed of light. And at the leading edge of this radiation sphere are
the McCarthy hearings and the Howdy Doody show. No wonder the ETs have
left us alone!

Roy Lewallen, W7EL

What was wrong with Howdy Doody?

tom
K0TAR

HFTA-ARRL-Space
 

On Sat, 01 Jul 2006 16:11:42 -0700, Richard Clark
wrote:


On the other hand, at HF the ratio between reflection and refraction
varies. There are times when both occur. During those times the
portion of the incident ray that is reflected returns to earth, while
the portion that is refracted continues on through the ionosphere into
space and never returns. I'm not sufficiently knowledgeable on the

But is it actually reflection?

Owen
--

HFTA-ARRL-Space
 

On Sat, 01 Jul 2006 18:32:46 -0400, jawod wrote:
This I don't understand. To me, refraction versus reflection IS the
issue. In optics, Brewster's angle is used. I still don't quite
understand thte PseudoBrewster's Angle...it seems to have a different
definition (at least in the ARRL book).

Hi John,

Perhaps you should offer that definition as its application seems to
be quite rare, and paired with some obscurity to the world of
sub-atomic dispersion.

I guess I was trying to get at how much ham radio is propagated into
space. Certainly SOME does.

SOME about covers it (you want that specified in dB?). I suppose by
your other references to SETI you are wondering about the chances of a
QSO in the same frequency from the other side of that ionospheric
curtain.

Given the odds, one frequency is as good as the next....

How does this compare to that amount propagated into space by Broadcast?

There you have to consider the magnitude of flux, continuously, over
the years. If the broadcasting is from Fox news (or any Murdoch
source for that matter), it will be indistinguishable from pinko
noise.

73's
Richard Clark, KB7QHC