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
--

"Owen Duffy" wrote in message
...
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?

no, it is actually a refraction. but it is useful sometimes to model it as
a reflection from a slightly higher level. that makes computation of angles
of incidence and height a bit easier.

But is it actually reflection?

no, it is actually a refraction. but it is useful sometimes to
model it as
a reflection from a slightly higher level. that makes computation
of angles
of incidence and height a bit easier.

============================================
The trigonometry is quite simple. Things become complicated when the
reflecting layer is not horizontal, ie., the layer is tilted.

The angle and direction of tilt are very difficult to predict.
Consequently, where on the surface of the Earth a ray returns is
anybody's guess.

This makes the vertical take-off angle, reported by antenna modelling
programs, even less useful.
----
Reg.

"Reg Edwards" wrote in message
...

But is it actually reflection?

no, it is actually a refraction. but it is useful sometimes to
model it as
a reflection from a slightly higher level. that makes computation
of angles
of incidence and height a bit easier.

============================================
The trigonometry is quite simple. Things become complicated when the
reflecting layer is not horizontal, ie., the layer is tilted.

The angle and direction of tilt are very difficult to predict.
Consequently, where on the surface of the Earth a ray returns is
anybody's guess.

This makes the vertical take-off angle, reported by antenna modelling
programs, even less useful.

no, it doesn't make it less useful. as a statistic it is still good, but
you have to remember that it is nothing more than a statistic. and everyone
knows 'you can prove anything with statistics'. the fact that the
ionosphere is more complicated than a horizontal reflection layer model
represents doesn't mean that its usefulness is reduced, just that there are
some cases when it won't be completely accurate... those are the fun things
that happen with propagation that keep it interesting.

Dear Reg:

You have articulated one of the many reasons why HF propagation is
described in stochastic terms. As you know very well, measurements or
predictions comprise at least two numbers: the best estimate of the number
and an estimate of the uncertainty of the first number. Present models of
HF propagation, which include antenna characteristics, provide both numbers.
Early models of HF propagation tended to be somewhat deficient in providing
the second number.

However, I remember using the early models to predict (extrapolate) in
real-time how much longer a certain frequency was likely to remain usable
from noting the drop-out of a higher frequency. The physics involved has
been understood for many years. It takes a long period of data gathering to
be able to do a good job with the second number.

In the early days (post WW2) of radio astronomy, the uncertainties of
some important measurements were greater than the estimate. That did not
last.

73 Mac N8TT

P.S. Nice to know that W2DU is back.
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Reg Edwards" wrote in message
...

But is it actually reflection?

no, it is actually a refraction. but it is useful sometimes to
model it as
a reflection from a slightly higher level. that makes computation
of angles
of incidence and height a bit easier.

============================================
The trigonometry is quite simple. Things become complicated when the
reflecting layer is not horizontal, ie., the layer is tilted.

The angle and direction of tilt are very difficult to predict.
Consequently, where on the surface of the Earth a ray returns is
anybody's guess.

This makes the vertical take-off angle, reported by antenna modelling
programs, even less useful.
----
Reg.

Dave wrote:
"Owen Duffy" wrote in message
...

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?


no, it is actually a refraction. but it is useful sometimes to model it as
a reflection from a slightly higher level. that makes computation of angles
of incidence and height a bit easier.


If the end result is that the wave returns back to earth, why is this
not termed reflection? Even if it is the result of several and/or
continuous refractions that result in a return of the wave from the 2nd
medium to the 1st, i.e., they sum to result in a reflected angle, seems
to me reflection is a good term.

I understand that a curved surface is more complex but if the result is
the same, ...?