"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)

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

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

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

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