> I respectfully beg to differ. The original Beverage was
developed
> to receive LF and VLF signals via groundwave. The lossy
ground
> caused the wave to "tilt" and hence it was able to induce
a signal
> into the horizontal Beverage wire.
OK, that's one explanation for the wave. It's really just a
way of saying the soil has loss.
We have the same effect with verticals, and the effect works
on 30MHz as well as on 30kHz. It actually is MORE pronounced
as we go up in frequency.
That does not explain the antenna pattern however, and the
antenna pattern is what actually determines S/N ratio and
sensitivity.
The situation on HF is different
> as the ionosphere supplies the wave tilt in most cases. It
might
> actually be an advantage to make the antenna "deaf" to
groundwave
> signals in those cases where there is a strong local
broadcast
> station.
I don't think so.
When ground conductivity gets high below the antenna the
close spacing between the antenna and the ground causes the
horizontal area to mostly just go dead. This is because the
"image" of the antenna is out-of-phase with the actual
antenna, cancelling any signal. At the same time the resonse
of antenna vertical ends are enhanced. The is the same
effect that makes a Flag or Pennant work, and why an EWE
only works over a good ground.
The conductor below the antenna can only have low
connectivity resistance if it removes ground losses. If it
has an effect, it is a negative effect becuiase the ONLY
effect would be to reduce sensitivity of the horizontal
wire.
What saves everyone subscribed to the concept that adding
the wire is a "good thing" is that losses in the ground
couple to the "ground wire" and in a few short feet the ESR
is high enough to not destroy the antenna pattern.
> My understanding of the wire under the beverage was that
it stabilizes
> the impedance when the ground conductivity changes (after
rain for
> instance). A stable impedance makes for stable nulls.
In order for the wire to stabilize impedance it must become
the primary groundplane for the antenna, rather than the
lossy earth around the antenna. Otherwise it cannot
stabilize antenna impedance.
If the wire (this would have to be magic) becomes the
primary groundplane, you now have an elongated loop antenna
and the log close-spaced horizontal sections cancel. Again
you enhance the end-response in relation to the desired
horizontal section.
An example of this is all the DXpeditions that try Beverages
at locations where saltwater is under the antenna. They come
away swearing at the antenna, rather than a swearing by it.
Another example is found if you change the ground to perfect
under a Beverage in a modeling program. Look at the pattern
and response.
I'm afraid no matter how you look at it adding the wire
can't possibly be a good thing, because it can only move the
antenna more towards behavior over a perfect groundplane.
Everyone who has used Beverages in a variety of environments
knows over wet very conductive earth Beverages quit
working, and if the soil is dry they are fine. Give me a
good reason why I want to move the antenna in that direction
when the ground is dry by adding a groundplane below the
antenna?
The thing that saves everyone who subscribes to the idea
that the wire helps is that is so tightly coupled to the
lossy earth it has extremely high loss over it's length.
73 Tom
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