Topband: Noise and reception

[k3ky@erols.com]

Hi, Tom-
It does not bother me that the horizontally-polarized *ground wave*
does not exist/ is not supported by the earth. I am trying to receive
horizontally-polarized *skywave* signals, and to the maximum
extent possible, reject all vertically-polarized signals, including
noise. There is a very big difference between the idealized (?)
elevation pattern published by K6STI and the one you describe,
which is that of a 'cloud warmer'. I can't help believing that my
antenna must be accomplishing this, at least to some degree.
A lot of 80/160 prop is apparently at high angles FWIW.
Also, K6STI said the antenna worked about as well at 10 feet
and 50 feet, i.e. that there must not be very much change in
the shape of the elevation plot as height is varied (?) He
actually addressed signal strength vs. height, however, if I
remember right. Is 10 feet a "few feet above earth" or not?
That was the height of his and my antenna. Sounds like you
advise putting your well-balanced loop a lot closer to earth in
order to demonstrate the major signal dropoff. I bet it still
picks up fairly well at 10 feet.
Another thought- if I take a half wave dipole or a full wave
(large) loop and put it very close to earth, 5-10 feet, it does not
go deaf. It is a cloud warmer, of course, and makes a good
NVIS antenna. It does receive horizontally-polarized skywave
signals, I bet. Why can't a mid-size loop receive horizontally-
polarized skywave signals? If I don't pick it up and turn it 90
degrees to vertical, why should it have much response to
vertical polarization simply by virtue of being close to the
earth? I can't see why that should be.    73, David K3KY

On 17 Feb 2002 at 2:01, Tom Rauch wrote:
  (snip) 
> For those of us with small well-balanced loop antennas, I'd like to
> suggest a little experiment. 
> 
> Take the small loop antenna and lay it over flat near the earth's
> surface, and watch the general levels of all signals. What you will
> see is a properly balanced loop just about goes dead, or at least has
> a very major reduction in sensitivity, when laid flat a few feet above
> earth.
> 
> The reason for this is simple. The earth effectively "short  circuits"
> the horizontally polarized electric field. The loop, Beverage,
> Pennant,  Flag, and even the K6STI antenna don't like to respond to
> horizontally polarized signals because of the earth. There just isn't
> much horizontally polarized signal there, if the earth has any
> reasonable conductivity. What horizontal component there is mainly
> comes from very high wave angles!
> 
> On the other hand, vertically polarized signals are re-enforced by the
> earth. Antennas near earth "want" to hear vertical signals, because
> the earth tends to re-enforce vertically polarized signals and cancel
> horizontally polarized signals.
> 
> Actually, this is also the very reason ground wave propagation 
> must be vertically polarized, and why the noise that propagates 
> along the earth for a distance is all vertically polarized.
> 
> We might wish otherwise, but we can't have mother earth treat one
> antenna in some special way! 
> 
> We aren't being unfair or pessimistic in telling the truth.
> 73, Tom W8JI
> W8JI@contesting.com