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