"Spike" wrote in message
...
On 08/03/15 09:33, Jeff wrote:
Spike wrote

I think you are coming at this from the wrong view point.

Perhaps the question that you should be asking is what take-off angles
are required to produce maximum ground wave, and how do you maximize
that for a MF mobile installation.

I'm really after figures for the proportions of the RF power fed to that
antenna, that finish up in whatever 'they' are called (the use of the
well-known word 'waves' seem to upset people despite their having been
used for the specifics I mentioned, for about 100 years).

I'm aware that reconfiguring the set-up might affect these proportions,
but I did refer the original query to a typical /M (mobile) set-up of a
short rod antenna not connected to ground and operating over average
conductivity in the MF/low-HF bands.

For example, does 40% power the sky (redacted), another 40% power the
space (redacted), and the other 20% power the surface (redacted)? Clearly,
100% of the RF power goes somewhere, and the various parts of it must add
up to 100% - so what are the proportions?

If the /M (mobile) set-up was changed to a /P (portable) one with a 5/8
lambda ground-mounted antenna, the sky (redacted) proportion would lower
and the surface/space (redacted) would increase - but from what to what?

I'm beginning to think that this topic is either so simple or so complex
that most Amateurs have either forgotten it or have never heard of it.


I think that Jeff may be on to something. What you need to do is download
one of the antenna modeling programs. Set it up for the antenna type you
want. Then you can look at the patten and see the take off angle. The take
off angle is what determins the ammount of power you have the differant
types of propogation.

On 08/03/15 14:22, Ralph Mowery wrote:

I think that Jeff may be on to something. What you need to do is download
one of the antenna modeling programs. Set it up for the antenna type you
want. Then you can look at the patten and see the take off angle. The take
off angle is what determins the ammount of power you have the differant
types of propogation.

That's an interesting thought, and one that had crossed my mind.
However, modelling is only as good as the modeller, and if things are
set up to model only the sky-wave component, I might not get the sort of
information I'm looking for. BICBW, as I've no experience of this.

However, I've just recalled that while researching the topic some time
ago, I came across some polar diagrams for cross-field antenna trials in
Egypt, which showed the ground/surface wave components as well as the
sky wave, the idea being for the MF broadcast band to maximise the
former and minimise that latter. Sadly, I didn't keep the url, but it
looks like it might be possible to determine some measure of the
relative power/field strengths. I'll see if I can find those diagrams,
the model used might have been mentioned.


--
Spike

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

"Spike" wrote in message
...
However, I've just recalled that while researching the topic some time
ago, I came across some polar diagrams for cross-field antenna trials in
Egypt,

Take them with a pinch of salt for the trials were discredited because they
were conducted withing the near field of a broadcasting mast, ISTR

Spike wrote:
On 08/03/15 14:22, Ralph Mowery wrote:

I think that Jeff may be on to something. What you need to do is download
one of the antenna modeling programs. Set it up for the antenna type you
want. Then you can look at the patten and see the take off angle. The take
off angle is what determins the ammount of power you have the differant
types of propogation.

That's an interesting thought, and one that had crossed my mind.
However, modelling is only as good as the modeller, and if things are
set up to model only the sky-wave component, I might not get the sort of
information I'm looking for. BICBW, as I've no experience of this.

It is obvious you have no experience.

Antenna modeling programs DO NOT MODEL PROPAGATION.

Antennas have little to no direct relationship to propagation modes other
than putting a main lobe where some particular propagation mode may or
may not exist at some particular frequency at some particular point in
time.


--
Jim Pennino

On 08/03/15 18:08, Jeff wrote:

Spike, you seem to think that there are different components coming from
the antenna that make up the sky-wave component and the ground wave.
That is not correct the antenna only radiates one kind of wave (EM).
Whether it finds its way to the receiver by sky-wave or ground wave is
purely due to what angle the wave hits the atmosphere/ground, and the
state of the atmosphere.

As an Example take a transmission on top band; during the day normally
there will be virtually no sky-wave propagation; use exactly the same
set up during the night and there will be considerable sky-wave.

I think I knew that, Jeff...

If your question is what do you have to do to maximize the ground wave
the it is obviously to keep the maxima in the polar diagram as low as
possible and don't waste power shooting it at high angles.

No, I know how to do that. What I'm after is the relative amounts of
power that finish up at the ionosphere, travelling through the
atmosphere, and travelling along the surface, for a typical mobile set-up.

Of course that is easier said than done, particularly with a mobile
where the ground is likely to be poorer than a fixed station with a good
ground mat.

My initial conditions were a ground of average conductivity.

Using something like NEC to model antennas will show the effects of
various antenna configurations and ground configurations on the low
angles of radiation.

But it's only a model, and results depend on how it was constructed.


--
Spike

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

"Spike" wrote in message
...

What I'm after is the relative amounts of power that finish up at the
ionosphere, travelling through the atmosphere, and travelling along the
surface, for a typical mobile set-up.


Which is, after all, quite a reasonable line of enquiry for any
self-respecting _REAL_ radio amateur, but perhaps the thread has
developed in an unfortunate direction because of the characterisitics
of questions posed off-the-cuff and not as a reasoned thesis?

(I know that I have fallen iinto that trap on a number of occasions)

Spike wrote:

On 08/03/15 18:08, Jeff wrote:

Spike, you seem to think that there are different components coming from
the antenna that make up the sky-wave component and the ground wave.
That is not correct the antenna only radiates one kind of wave (EM).
Whether it finds its way to the receiver by sky-wave or ground wave is
purely due to what angle the wave hits the atmosphere/ground, and the
state of the atmosphere.

As an Example take a transmission on top band; during the day normally
there will be virtually no sky-wave propagation; use exactly the same
set up during the night and there will be considerable sky-wave.

I think I knew that, Jeff...

If your question is what do you have to do to maximize the ground wave
the it is obviously to keep the maxima in the polar diagram as low as
possible and don't waste power shooting it at high angles.

No, I know how to do that. What I'm after is the relative amounts of
power that finish up at the ionosphere, travelling through the
atmosphere, and travelling along the surface, for a typical mobile set-up.

Of course that is easier said than done, particularly with a mobile
where the ground is likely to be poorer than a fixed station with a good
ground mat.

My initial conditions were a ground of average conductivity.

Using something like NEC to model antennas will show the effects of
various antenna configurations and ground configurations on the low
angles of radiation.

But it's only a model, and results depend on how it was constructed.

I would rephrase your original question as follows. The approximate
signal strength of the space wave at a certain distance, assuming a
fairly low angle of the main lobe of the aerial with a moderate amount
of gain over isotropic, can be calculated from simple physics. At
about the same distance (and where of course you are not likely to see
the space wave unless you have a very tall pole, but it has a defined
signal strength well above you), what is the likely signal strength of
the ground wave? Is it very much lower due to poor coupling, losses
etc.? Is it about the same? Or is it much higher due to some
phenomenon which I can't explain at the moment? That is really the
same question as the one you asked (I think!), but couched in practical
and testable terms.

(It is rather trying to see the ignorant mocking a perfectly reasonable
question from a position of total incomprehension. A bit juvenile,
methinks.)

--
Roger Hayter