Topband: Ground mounted 1/2 wave

[Tom W8JI]

> We both agree that the .38 db increase is at all elevation angles since 
> the increase in efficiency at the feed doesnt change the pattern shape, 
> just levels. OK ?

There you say pattern shape does not change, and the change is uniform at 
all angles.


> Where the differences are is in the initial far field signal strengths 
> from zero to lets say 20 degrees. With a perfect theoretical ground the 
> levels are the same.

There you say pattern shape changes (has differences) from zero to 20 
degrees.

Which is it?

>If that held in reality then no matter what the ground losses are the BC 
>stations would not be spending the big bucks in radial fields, even for 1/2 
>waves.

FCC rules say broadcast stations must **either** install at least 90 quarter 
wave radials, **or** do expensive time consuming efficiency proofs and 
submit paperwork for it proving field strength is as expected.

> The city lot ham would be readily competitive with the antenna farm 
> operator or the little guy in a coastal salt water swamp.

That's absolutely true on transmit if the city lot Ham has a 250-foot tower, 
and the surroundings of his city lot are similar flat open fields without 
power lines, buildings, and other things.

Even in a bad situation, like a 60 foot tall inverted L and severely 
truncated radial system, a local Ham on 160 on a corner city lot was 
consistently within a few dB of my 1/4 wave vertical in black wet swampy 
soil. His antenna was a current-fed short Marconi, so we should reasonably 
expect a 1/2 wave to be even closer.

> My point all along is that ground losses change the shape of the main lobe 
> curve at low elevations and reduce signal levels there.

First you say this:

> We both agree that the .38 db increase is at all elevation angles since 
> the increase in efficiency at the feed doesnt change the pattern shape, 
> just levels. OK ?

Now you say this:

> My point all along is that ground losses change the shape of the main lobe 
> curve at low elevations and reduce signal levels there.

Which is it? It cannot be both.


>Total power doesnt change but it is no longer all radiated, some is now 
>dissipated in the lossy ground. Basic physics tell us you cant have both at 
>the same time.

Basic EM theory says the majority of loss in the nearfield is due to 
induction fields, both electric and magnetic.

EM radiation, which is what allows force on charges at a distance, is a weak 
force near the antenna. It simply decays at a slower rate, and because the 
behavior is quite different the behavior of induction fields, radiation goes 
on long after the induction fields are gone.

Changing energy storage field losses (induction field losses) changes 
efficiency. Radiation pattern in a vertical is formed and changed many 
wavelengths out.

When we change radials near a vertical antenna, we change conducted 
feedpoint losses and induction field losses. The effect on radiation is 
mostly as if we simply made 200 feet (or whatever) of the path distance a 
better path. There is a slight change on pattern, but because radiation 
field intensity is low it isn't much of a change.

Now we could locate near a large saltwater body in the path, and have 
significant improvement at low angles, but that is because miles of the path 
are better....not just 200 feet of it.

We might want it to be different and be able to add wire and make clay into 
saltwater, but unfortunately that is not how it works. Unless we can change 
soil conditions for miles out, or add a ground that radiates, we cannot 
affect elevation  pattern or low angle field strength very much.

This is old stuff, it is repeated in different ways by many different 
independent sources, because that is just how it works. Only in the fantasy 
world of Ham radio or CB do we find controversy, and the controversial ideas 
are never backed by more than opinions. Some Hams will insist forever that 
radials change patterns by reducing TOA, and it will even appear in 
scholarly places like eHam articles. It won't appear in peer reviewed 
engineering textbooks.

73 Tom