E/M radiation from a short vertical aerial
 

On 08/03/15 20:06, wrote:
On Sunday, March 8, 2015 at 3:40:21 AM UTC-5, Spike wrote:
On 08/03/15 00:17, wrote:

True ground wave, which to me, is the same as the surface wave,
actually can follow the curvature of the earth, which a space wave
cannot do. But true ground or surface waves are generally only
taken advantage of on the lower frequencies such as MW, or LW.

That's true, which is a shame as useful ground-wave/surface wave can be
had on 28 MHz; a maximum range figure for a path over ground of average
conductivity might be 25 miles, and considerably more if the path is
over water (especially sea-water).

That's space wave on 10m. Even seeing a surface wave on 40m is a bit
of a stretch from the norm. As I mentioned in my 2nd post, the reason
I saw farther than expected from space wave operation on 40m, could
well have been due to refraction of the space wave, and due to the fact
that the radio horizon is farther than the visual horizon.

I used to work local 10m all the time back in the 80's, early 90's..
25 miles is fairly easy with any decent antenna, at a decent height
above ground. I used to work a good bit farther than that fairly often,
when using an antenna at 35-45 feet up.



The reason I think so, is because the distances I could work with it
were a good bit farther than what I would expect with the space wave
alone.

Maximum surface wave over ground with average conductivity might be 40
to 45 miles on 40m; if you were getting ranges over this, then your
ground conductivity might have been enhanced, or due to the height of
your ground-plane, you could have experienced refraction of the space
wave. If your location was on a hill-top or other high ground, this
could have helped the space wave refraction as well.

The ground is good here,

With respect, the difference in local ground is rather over stated.

Taking the US as an example, the conductivity ranges from 0.5mS to 30mS,
which sounds a lot. However, compared to sea water, 5000mS, it is all
rather poor.

I noticed this some years back when reading a paper, as I recall written
by the US Navy, which played down the importance of ground conductivity,
other when either at sea or in close proximity to the shore.

There is a world atlas of conductivity which is on the web, I can't
recall the URL, but it is worth looking out. The various seas and oceans
do vary, I recall the Baltic being less conductive for example.
Likewise, some of the patterns in the various countries are rather
intriguing. Some areas you would expect to be conductive are not. I
assume due to local rock formations etc.

E/M radiation from a short vertical aerial
 

On 3/8/2015 7:21 PM, Brian Reay wrote:

There is a world atlas of conductivity which is on the web, I can't
recall the URL, but it is worth looking out. The various seas and oceans
do vary, I recall the Baltic being less conductive for example.
Likewise, some of the patterns in the various countries are rather
intriguing. Some areas you would expect to be conductive are not. I
assume due to local rock formations etc.

I've been lurking in this thread and it reminded me of a time many years
ago when I was working on a receiver setup. A colleague gave me a book
with an equation for signal strength of a signal in the cell phone
frequency range in various terrestrial environments. I had a little
trouble accepting an arbitrary equation that wasn't at least close to
the typical 1/r^2 formula in free space. I seem to recall there was no
1/r^2 term at all rather it was more like a linear or maybe had a
rlog(r) term.

In any event, no one could explain where the equation came from. I
suppose it was an empirical equation rather than something derived from
theory. Ignoring waves bounced off the upper atmosphere, I assume the
earth acts to help focus the signal and strengthen it close to the ground?

--

Rick

E/M radiation from a short vertical aerial
 

On 3/6/2015 6:02 PM, 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.

Three different waves will be launched from this: the sky wave, the
space wave (including the reflected ray), and the surface wave. Each of
these have their own characteristics, inasmuch as the sky wave is
launched willy-nilly even if the band isn't open for that mode, the
space wave depends on the path to the receiver, and the surface wave
depends on the electromagnetic characteristics of the air and the
surface material, although to some extent the latter affects all the
waves generated.

My question is: since all these result from the emission of RF from the
short rod antenna, what proportions of the total RF power supplied to it
are found in each of these three separate waves, and what factors
control these proportions?

I found a reference that says 100% of the signal from an antenna goes
into the sky wave, space wave and the ground wave. None of the signal
is lost in the transmission process after leaving the antenna. ;)

--

Rick

E/M radiation from a short vertical aerial
 

On 3/8/2015 4:17 PM, Stephen Thomas Cole wrote:

Spike, you're a gormless ****. Seriously, you're giving Gareth Alun Evans
G4SDW a run for his money here.

I can see you are right in the running yourself...

--

Rick

E/M radiation from a short vertical aerial
 

On 3/8/2015 6:56 AM, Spike wrote:
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).
....snip...

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 everyone understands the question just fine. But it is a
question without an answer.

What you are asking is when you feed a bird, how much of that feed
produces crap that lands on your car based on the composition of the
feed? If the feed has more fat and less protein does that put more crap
on the car or the driveway?

--

Rick

E/M radiation from a short vertical aerial
 

On Sunday, March 8, 2015 at 6:21:06 PM UTC-5, Brian Reay wrote:

The ground is good here,

With respect, the difference in local ground is rather over stated.

Maybe so, but not really by me. :|

Taking the US as an example, the conductivity ranges from 0.5mS to 30mS,
which sounds a lot. However, compared to sea water, 5000mS, it is all
rather poor.

Sure. It's rated at 30mS here, which was why I said it was "good".
And I'm about 55-60 miles from the Gulf of Mexico. I've run mobile from the
beach, one time actually backing up to the water and running ground wires
into the ocean. Needless to say, my 14 ft tall mobile whip was browning
the food quite nicely on that occasion. :) On the Ford truck it was on,
it does pretty well even over poor ground, but it really got with the
program down at the beach. I was parked at the mouth of the Brazos River
down at Quintana Beach. I was also fishing.. I'd rig up my rod and reels,
putting them on auto pilot, and then would kick back and drink brewed
beverages while jibber jabbering on the radio. :) Mostly 40 and 80 meters.
If I saw a rod start to twitch, I'd put down the mike and adult beverage,
and reel in the fish. :)


I noticed this some years back when reading a paper, as I recall written
by the US Navy, which played down the importance of ground conductivity,
other when either at sea or in close proximity to the shore.

I've never really worried about it too awful much. I don't really rely
on it, one way or the other. Even with decent ground quality, I still
run a good radial set, or if elevated, enough radials to do the job,
as if the ground were poor. Of course, I can't control the ground
conductivity away from my QTH. So no use worrying about it.


There is a world atlas of conductivity which is on the web, I can't
recall the URL, but it is worth looking out. The various seas and oceans
do vary, I recall the Baltic being less conductive for example.
Likewise, some of the patterns in the various countries are rather
intriguing. Some areas you would expect to be conductive are not. I
assume due to local rock formations etc.

The only map I've seen is one that is in the ARRL handbooks.. It's the
one that shows this area as 30 mS. I think it only covered the US, or
maybe North America at the max.. Don't know about the rest of the planet.

E/M radiation from a short vertical aerial
 

rickman wrote:
On 3/8/2015 4:17 PM, Stephen Thomas Cole wrote:

Spike, you're a gormless ****. Seriously, you're giving Gareth Alun Evans
G4SDW a run for his money here.

I can see you are right in the running yourself...

Hey, I'm not the one with the fundamental misunderstanding of radio theory
after 50+ years in the hobby.

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

E/M radiation from a short vertical aerial
 

On 3/9/2015 2:26 AM, Stephen Thomas Cole wrote:
rickman wrote:
On 3/8/2015 4:17 PM, Stephen Thomas Cole wrote:

Spike, you're a gormless ****. Seriously, you're giving Gareth Alun Evans
G4SDW a run for his money here.

I can see you are right in the running yourself...

Hey, I'm not the one with the fundamental misunderstanding of radio theory
after 50+ years in the hobby.

The problem has nothing to do with radio theory.

--

Rick

E/M radiation from a short vertical aerial
 

On 09/03/15 00:14, rickman wrote:
On 3/8/2015 6:56 AM, Spike wrote:

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 everyone understands the question just fine. But it is a
question without an answer.

But that *is* an answer!

What you are saying is that the research remains to be done.

What you are asking is when you feed a bird, how much of that feed
produces crap that lands on your car based on the composition of the
feed? If the feed has more fat and less protein does that put more crap
on the car or the driveway?

I'd say, based on that, that nutrition science is better understood than
the e/m fields emitted by an antenna.


--
Spike

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

E/M radiation from a short vertical aerial
 

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