Topband: Let's try stuff

[Tom Rauch]

Hi Steve,
 
> VK6VZ replied:
> Rex ZL3REX is considerably farther from the geomagnetic equator than
> VK6 - at a higher latitude where the power coupling into the
> ionisphere very definitely favours a vertically polarised antenna.

ON4UN's book in section 2.5 "postulates" coupling to the 
ionosphere near the equator is *less* for horizontals. No where do 
we find a statement that it is xx dB, and the text even qualifies the 
statement horizontals might be more favorable at some magnetic 
latitudes by saying for useful antennas "for dipoles we are talking 
about heights more than 1/2 wl".

When I look at VK6 in fig1-19, it is not too much different than ZL. 
Areas like DU, 9M2, and PY are on the geomagnetic equator.

My point is we sometimes lay all results to one or two things, 
when it can be tiny parts of many many things, none of which in 
themselves are major at all.  

For example, we can not toss out the impossible task of getting a 
decent wave angle out of a horizontal antenna, nor can we toss out 
the fact that clutter around the antenna has a great effect.

> Bob VK3ZL is at a similar latitude to myself (although at slightly
> higher one), where the power coupling JUST favours a vertical antenna.
>  However, the soil conductivity in Victoria is generally MUCH better
> than in Western Australia, so his far field losses are likely to be
> several dB less than mine.

Farfield losses do not change that much unless we make a drastic 
change like moving to saltwater. The difference between the 
poorest soils and best is a factor of perhaps thirty, while most are 
considerably less than that difference. Saltwater is thousands of 
times more conductive than soil, yet verticals do not suddenly 
switch-off when moved from a ship to rocky thin soil and hills like 
we find in New Zealand. Copper is hundreds or thousands of times 
better than saltwater, yet N6RK barely measured a change when a 
fixed antenna had copper laid out for many many wavelengths!   

What we see in programs like EZnec are the results at a distance 
of hundreds of wavelengths over flat homogeneous earth, and I 
think that exaggerates what we picture as happening. If it did, we 
would never work anyone except coastal stations.

What actually happens is the slope of attenuation changes and as 
we view a system at large distances the total attenuation is much 
different along the earth. I can give a good practical example of this.

If you model a vertical over poor soil you will see nearly ZERO field 
strength at zero degrees. This is in spite of the fact we know we 
can hear BC stations for 25 miles or more on groundwave. We also 
know within a few miles of the antenna there is very little difference 
in FS at 20 degrees or along the ground!

When the distance the model uses to predict pattern becomes 
large compared to height of the ionosphere and curvature of the 
earth, we can not rely on attenuation shown in the pattern.

I do not think we can consider there is a "switch" up in the 
constantly changing jumble of an ionosphere that suddenly does 
not permit a vertical to work with less than a 10 degree shift in 
latitude!!

I honestly can't find anything anywhere that says at xx degrees 
latitude, you can't use this polarization. As a matter of fact, the 
theories we hear are quite full of disagreements and contradictions.

If we read where paths are predicted, we see contradictions with 
results are pointed out. If we read the method of propagation, we 
see contradictions pointed out.

Too often we consider something a nebulous as what happens in 
that soup above as something concrete with clear boundaries. 
Remember, a theory only has to fail one test and we know it is 
wrong or incomplete.   

> ambient noise level is MUCH higher - because of the fact that the
> (mainly vertically polarised) noise propagates so much better.

Noise is predominantly vertically polarized exclusively because the 
earth attenuates any horizontal components. It is only ground-wave 
propagated terrestrial sources from the far-field that are 
predominantly vertical. 

Noise is absolutely no different than a desired signal so far as 
polarization when both propagate along the same path. Ionospheric 
noises from thunderstorms and distant noise sources are no 
different than desired signals in polarization. 

> The results that Tom W8JI sees from the antenna systems of ZL3REX and
> VK3ZL is what you would expect, given their magnetic latitude and
> ground conductivity.

While that sounds profound, I really think that is too simple. People 
who work in engineering will know exactly what I mean when I say 
the short clear easy to understand answer is often the most 
inaccurate answer!  

No one knows what the ground conductivity actually is or how it 
affects the signal at the useful wave angles, how much difference 
the small latitude change actually makes, or how efficient anyone's 
compromised antennas are. As a matter of fact, when we place 
two antennas 500 feet apart on 160 we have to be very careful to 
avoid interaction. When we place them within a dozen feet in a 
complex environment, we probably have no idea at all what is 
radiating and how much!  

We often try to take a vastly complex system with many shades of 
gray, and make it into black and white.

My point is not to disagree with your results, but rather to point out 
without knowing much more we can not reach any conclusion 
about WHY you have the results you do. Certainly nothing I can 
find in the text on "Polarization coupling" indicates it behaves like a 
switch.
73, Tom W8JI
W8JI@contesting.com