On Thursday, March 12, 2015 at 1:43:04 PM UTC-5, Spike wrote:

I asked a simple and straightforward question.

It's not that simple and straightforward though.. Best way to get
some idea would be to model the antenna, and note the gain at the
usual angles to be used for the various types of propagation.
And being as skywave will depend on many different angles for the
different bands at different times of day... :+
That makes it even more complicated. Space and surface wave will
depend mostly on the lower angle performance. Modeling the antenna
over ground of average conductivity, and then deciding what angles
are likely to be used for each type of propagation, and then noting
the modeled gain at those various angles is going to give you a
better idea than anything we can tell you. :|

Spike wrote:
On 12/03/15 13:28, Brian Reay wrote:
Spike wrote:
On 06/03/15 23:02, Spike wrote:

Imagine a short rod vertical aerial not connected to ground, for the
(say) 160/80/60/40m bands, as might be found in a typical /M set-up, fed
with RF energy and operating over ground of average conductivity.

Many thanks to all who took the trouble to reply, with input ranging from
from the uncouth through the unhelpful to the deeply technical. The
modelling results and the graphs of the surface-wave propagation that
were provided will likely prove very useful for another propagation
project currently under study here.

One fact that has become apparent is that ground conductivity maps that
assign a value to region-wide areas are not to be trusted - there are
sometimes quite severe changes in local conductivity, and these could
encompass the ground that affects the radiation pattern from one's
antenna. However, models have now become sophisticated enough to
incorporate these into their predictions; the difficulty lies in
obtaining reliable conductivity figures for one's location, especially
those of poor conductivity where earth currents can run deep in the soil.
Although this isn't strictly an 'antenna' issue, it is nevertheless
fundamental to LF/MF/HF operation and highly pertinent as to how the
antenna contributes to the station performance.

While your local earth conductivity may well vary from that for you region,
in the scheme of things, especially if the path in question includes a
transit of sea water, to suggest it will play a significant role is
somewhat bold. To see this, look at the relative numbers I gave earlier for
North America.

If you understand what I wrote above, you'll see my point was about local
conductivity and how it affects the radiation pattern after being
launched from an antenna, rather than the variability along a signal
path, although I did mention for completeness that models can now take
such variability into account.

Local conditions will, of course, impact antenna efficiency.

The antenna efficiency is affected by its mechanical form. Earth losses
are something else, which can be factored in to estimate antenna system
efficiency, which, of course, isn't the same thing.

I suggest you do some more thinking before you challenge the work of
eminent people who have studied this area and published papers etc.

I asked a simple and straightforward question, which has been answered
only in part and not at all by you, in what appears to be your normal
spirit of offering every assistance short of actual help. As you mention
published papers, perhaps you'd let us know how many of yours have seen
the light of day in peer-reviewed prestige journals?

I find it difficult to accept input on this and similar matters from
someone who not only avoided taking out an HF licence for 30 years but
who also judges the finer points of HF receiver performance by noting
which DXpeditions might be subsidised by which manufacturer.


You are Gareth Alun Evans G4SDW AICMFP!

--
STC // M0TEY // twitter.com/ukradioamateur

On 13/03/15 07:30, Jeff wrote:

If you understand what I wrote above, you'll see my point was about
local conductivity and how it affects the radiation pattern after being
launched from an antenna, rather than the variability along a signal
path, although I did mention for completeness that models can now take
such variability into account.

I think it is your choice of words that is causing the confusion. It is
not normally the practice to consider the ground conductivity over the
entire transmission path when considering the radiation pattern of an
antenna. It is usual to have a 'local' radiation pattern and then
consider what happens on the path as a separate (path loss) issue.

Mmm...my original question was concerned with how much power wound up
where, I'm sure this sort of thing was asked after sky-wave propagation
was discovered ~90 years ago. I believe that ground-wave/space-wave
propagation was understood before then.

Obviously with a sky wave path the intervening ground has no effect, but
with a ground wave signal it can have a huge effect, particularly is
there is water in the path. The ground causes the lower portion of the
wave to be retarded so you can think of the wave-front as starting to
slope, the degree of additional slope along the path depends on the
ground properties (conductivity and permittivity) at any point. The wave
will propagate like this until the 'slope**' becomes too great an angle
for the wave to propagate.

Yes, I'm familiar with the concept, I've mentioned it several times
before now, usually in terms of an ultimate maximum surface-wave range.

Interestingly, the ITU ground-wave curves that were referenced in this
thread show no such phenomenon, even at 30 MHz, or suggest that this is
a much gentler in action than might otherwise appear - perhaps this
implies there is a limit to the veracity of the modelling?

**apologies to Jeremy Clarkson
..
I recall a cartoon about Spiro T. Agnew in the 1960s.....Unsurprisingly,
I can't seem to find a reference to it. I think it was published in Time
magazine, BICBW. Today, it's what's known as 'not politically correct',
the current version of doublethink applying here.

[1] Once upon a time, the group I worked in had brought in the UK's
leading theoretical electromagneticist to act as an adviser. Afterwards,
I buttonholed him and asked for his view on an e/m issue[2] I was
responsible for. It was a straightforward question, but he had
difficulty understanding it, nonetheless he said he'd look into it. He
got back to me two weeks later. In apologising for the delay, he said
that no-one had ever asked this question before, and he'd spent the
intervening time researching the issue. I'm well used to asking awkward
questions of experts, it's their replies that give them away as to
whether they know their stuff or not.

[2] related to what happens when an e/m wave meets a surface, so not
entirely disconnected from this thread. It's a subject one would think
would have been well covered, but apparently this was not the case, and
asking a simple question revealed that.


--
Spike

"Hard cases, it has frequently been observed, are apt to introduce bad
law". Judge Rolfe

Spike wrote:
On 13/03/15 07:30, Jeff wrote:

If you understand what I wrote above, you'll see my point was about
local conductivity and how it affects the radiation pattern after being
launched from an antenna, rather than the variability along a signal
path, although I did mention for completeness that models can now take
such variability into account.

I think it is your choice of words that is causing the confusion. It is
not normally the practice to consider the ground conductivity over the
entire transmission path when considering the radiation pattern of an
antenna. It is usual to have a 'local' radiation pattern and then
consider what happens on the path as a separate (path loss) issue.

Mmm...my original question was concerned with how much power wound up
where, I'm sure this sort of thing was asked after sky-wave propagation
was discovered ~90 years ago. I believe that ground-wave/space-wave
propagation was understood before then.

Obviously with a sky wave path the intervening ground has no effect, but
with a ground wave signal it can have a huge effect, particularly is
there is water in the path. The ground causes the lower portion of the
wave to be retarded so you can think of the wave-front as starting to
slope, the degree of additional slope along the path depends on the
ground properties (conductivity and permittivity) at any point. The wave
will propagate like this until the 'slope**' becomes too great an angle
for the wave to propagate.

Yes, I'm familiar with the concept, I've mentioned it several times
before now, usually in terms of an ultimate maximum surface-wave range.

Interestingly, the ITU ground-wave curves that were referenced in this
thread show no such phenomenon, even at 30 MHz, or suggest that this is a
much gentler in action than might otherwise appear - perhaps this implies
there is a limit to the veracity of the modelling?

**apologies to Jeremy Clarkson
.
I recall a cartoon about Spiro T. Agnew in the 1960s.....Unsurprisingly,
I can't seem to find a reference to it. I think it was published in Time
magazine, BICBW. Today, it's what's known as 'not politically correct',
the current version of doublethink applying here.

[1] Once upon a time, the group I worked in had brought in the UK's
leading theoretical electromagneticist to act as an adviser. Afterwards,
I buttonholed him and asked for his view on an e/m issue[2] I was
responsible for. It was a straightforward question, but he had difficulty
understanding it, nonetheless he said he'd look into it. He got back to
me two weeks later. In apologising for the delay, he said that no-one had
ever asked this question before, and he'd spent the intervening time
researching the issue. I'm well used to asking awkward questions of
experts, it's their replies that give them away as to whether they know their stuff or not.

[2] related to what happens when an e/m wave meets a surface, so not
entirely disconnected from this thread. It's a subject one would think
would have been well covered, but apparently this was not the case, and
asking a simple question revealed that.


LOL, you're taking this lampoon of Gareth a bit too far now, OM. Even he's
not *this* deluded.

--
STC // M0TEY // twitter.com/ukradioamateur

Jeff wrote:

If you understand what I wrote above, you'll see my point was about
local conductivity and how it affects the radiation pattern after being
launched from an antenna, rather than the variability along a signal
path, although I did mention for completeness that models can now take
such variability into account.


Spike

I think it is your choice of words that is causing the confusion. It is
not normally the practice to consider the ground conductivity over the
entire transmission path when considering the radiation pattern of an
antenna. It is usual to have a 'local' radiation pattern and then
consider what happens on the path as a separate (path loss) issue.

Ground conductivity more that a few wavelengths from the antenna has an
insignificant effect on the antenna pattern.

Ground conductivity around the antenna has a small effect on the antenna
pattern in the real world.

If you doubt this, download the free demo version of EZNEC and compare
the pattern of an antenna over average ground to an antenna over
poor ground.


--
Jim Pennino

Jeff wrote:
If you understand what I wrote above, you'll see my point was about
local conductivity and how it affects the radiation pattern after being
launched from an antenna, rather than the variability along a signal
path, although I did mention for completeness that models can now take
such variability into account.


Spike

I think it is your choice of words that is causing the confusion. It is
not normally the practice to consider the ground conductivity over the
entire transmission path when considering the radiation pattern of an
antenna. It is usual to have a 'local' radiation pattern and then
consider what happens on the path as a separate (path loss) issue.

Obviously with a sky wave path the intervening ground has no effect, but
with a ground wave signal it can have a huge effect, particularly is
there is water in the path. The ground causes the lower portion of the
wave to be retarded so you can think of the wave-front as starting to
slope, the degree of additional slope along the path depends on the
ground properties (conductivity and permittivity) at any point. The wave
will propagate like this until the 'slope**' becomes too great an angle
for the wave to propagate.


**apologies to Jeremy Clarkson


Jeff, Spike's too far down the hole he's dug to climb out now without
losing face, so I fear your assistance will be rejected.

--
STC // M0TEY // twitter.com/ukradioamateur

Brian Reay wrote:
Spike wrote:
On 06/03/15 23:02, Spike wrote:

Imagine a short rod vertical aerial not connected to ground, for the
(say) 160/80/60/40m bands, as might be found in a typical /M set-up, fed
with RF energy and operating over ground of average conductivity.

Many thanks to all who took the trouble to reply, with input ranging from
from the uncouth through the unhelpful to the deeply technical. The
modelling results and the graphs of the surface-wave propagation that
were provided will likely prove very useful for another propagation
project currently under study here.

One fact that has become apparent is that ground conductivity maps that
assign a value to region-wide areas are not to be trusted - there are
sometimes quite severe changes in local conductivity, and these could
encompass the ground that affects the radiation pattern from one's
antenna. However, models have now become sophisticated enough to
incorporate these into their predictions; the difficulty lies in
obtaining reliable conductivity figures for one's location, especially
those of poor conductivity where earth currents can run deep in the soil.
Although this isn't strictly an 'antenna' issue, it is nevertheless
fundamental to LF/MF/HF operation and highly pertinent as to how the
antenna contributes to the station performance.


While your local earth conductivity may well vary from that for you region,
in the scheme of things, especially if the path in question includes a
transit of sea water, to suggest it will play a significant role is
somewhat bold. To see this, look at the relative numbers I gave earlier for
North America.

Local conditions will, of course, impact antenna efficiency.

I suggest you do some more thinking before you challenge the work of the
eminent people who have studied this area and published papers etc.

I'm really in two minds as to whether this is all just a massive send up of
Gareth Alun Evans G4SDW or not. It's all there, the initial wrong-headed
query, the subsequent aggressive/dismissive response to those helpful souls
correcting the mistake, the rejection of long-established and
well-researched principles. It's got to be a wind up, Spike isn't this much
of a ****.

--
STC // M0TEY // twitter.com/ukradioamateur