Gary,
I understand also your view of the situation BUT, if this were true, then to
my view entire Beverage antenna concept would be destroyed. Why?
Because of the slope of a few degrees, both in the forward and reverse
directions, of the element as it sags between supports over the majority of
its length.
In the same vein, the "most simple Beverage" as described in ON4UN's book is
a single center support model with 1/2 its length being sloped upward and
the other 1/2 sloping downward.
If the theory you propose is correct, then this model is nothing but two
vertical elements. In practice this model works VERY well with just as much
side rejection as its more "textbook" siblings.
Also, the Beverage antennas constructed over sloping terrain, many with much
more slope than the 11 degrees we obtain with a 5x1 termination slope, work
very well.
As an example of this type of implementation, the Beverages I constructed on
Thaytay Khun Island for the XZ0A DXped in 2000 were nearly as far from
textbook as they could be. The island was small and the station area was
nearly 200 feet above the shoreline. Consequently the Beverage antennas
would for the most part start off one side of the island and carry across to
the other side.
They were supported above ground by laying them on the jungle foilage. In
one location a small canyon was crossed with the antennas utilizing azimuths
in that direction going down into the canyon and back up the other side.
My experience had taught me that this method is much less detrimental to the
performance of the Beverage than suspending the wire where it would be 25-30
feet above ground for a short distance. In my own home installation and at
other permanent installations I utilize 4 "ground" wires to form a grid
underneath my Beverage element when the antenna must cross small canyons.
This elevates the actual earth ground such that the Beverage does NOT appear
as a sky wire aerial. I could not do this in Burma.
Back to the subject. The XZ0A antennas were signal split and filtered to
feed separate selectors for use at the 40, 80 and 160 Meter stations. I
personally operated ALL of these stations during the 4 weeks of the DXped.
For our use, the antennas performed near textbook. We had electrical
interference from both the Burmese and Thai mainland cities approximately 5
miles distant. We had atmospheric noise from the south Pacific in the
direction of Australia.
In all cases, on all three bands, the directionality of the antennas was
superb. When using antennas that were at right angles to the noise sources,
the noises were not detectable to the detriment of even the lowest level
received signals.
In summary, I believe that as long as the slope of the antenna, whether the
main element or the sloped terminations, is maintained at less than 30
degrees from horizontal AND maintained within 10 feet or so of earth ground
influence, will have neglible pickup of normal level vertically polarized
signals from the sides.
By the same token, I believe that only a SHORT piece of truly vertically
installed wire as part of the element or the ground connection after the
termination resistor will GREATLY reduce the effectiveness of the Beverage
antenna from its intended use.
I am always in the learning mode and certainly do NOT know it all. I am
continually expermenting with "new" and different methods of installing
Beverage antennas. I have plans to try some of the sides of a mountain with
near 45 degree slopes BUT in the horizontal plane along the side of the
mountain.
Have a good day. Off to the salt mine for me. 73 de Milt, N5IA
----- Original Message -----
From: "K9AY" <k9ay@k9ay.com>
To: "Milt Jensen, N5IA" <n5ia@zia-connection.com>; <topband@contesting.com>
Sent: Tuesday, December 09, 2003 10:54 PM
Subject: Re: Topband: Cone of Silence
> Milt
>
> I still think my description of the constant vertical aperture is correct.
> The analogy of rotating an antenna ignores the increase in length of the
> wire segment from 10 feet to 50 feet. The projected vertical length is
> unchanged and will be exposed to the same total energy whether straight or
> sloped.
>
> But, with your (and other's) insistence that the technique works, there is
> another mechanism to explore -- phase shift over the length of the sloped
> section. This phase dispersion may very well play a more important role
> than I have assumed.
>
> 73, Gary
> K9AY
>
> > Thanks Gary, but my knowledge of the antenna physics and wavefronts
> dictates
> > otherwise. The vertical component in your 50' sloping termination from
a
> > 10' height does not have the same exposure to the vertically polarized
> > incidental wave as the single 10' vertical piece of wire.
> >
> > This is comparable to rotating an element from one polarity to the
other.
> > In the 5x1 example the angle of the sloping portion of the antenna
element
> > is only approximately 11 degrees off horizontal. At that angle there is
> > only approximately 27 percent of the energy of the vertical wave
available
> > for pickup. This is approximately a 6 dB improvement over the single
10'
> > vertical termination wire.
> >
> > Perhaps I am all wet in this one, but I don't think so. My experience
in
> > constructing and using numerous fields of Beverage antennas has shown
that
> > the theory is carried into actual operation with regard to the improved
> > attenuation of vertically polarized signals arriving from the sides.
> >
> > Milt, N5IA
> >
> > ----- Original Message -----
> > From: "K9AY" <k9ay@k9ay.com>
> > To: <topband@contesting.com>
> > Sent: Tuesday, December 09, 2003 3:25 PM
> > Subject: Re: Topband: Cone of Silence
> >
> >
> > > Sloping the ends of a Beverage is one of many antenna ideas that seem
> > > plausible, but do not hold up under further analysis.
> > >
> > > I know Tom W8JI has explained this before, but I'll try again...
> > >
> > > It doesn't matter whether you slope the last 50 feet of the Beverage
or
> > > continue 40 feet of it horizontal and run 10 feet straight down.
Either
> > way,
> > > you have 10 feet of vertical distance. A vertically-polarized
wavefront
> > > arriving from the side will 'see' only the 10 foot high vertical
> component
> > > of the sloped end -- the same as with a straight vertical wire.
> > >
> > > 73, Gary
> > > K9AY
> > >
> > >
> > > > Don and Tom,
> > > >
> > > > My understanding of the operational characteristics of the Beverage
> > > antenna
> > > > is that the use of sloping terminations eliminates the requirement
of
> > > > special efforts to cancel the reception of vertically polarized
> signals
> > in
> > > > ALL directions that would be picked up by a few feet of vertical
> > > termination
> > > > wire off a pole.
> > > >
> > > > I understand that the vertically polarized signals from the "front"
of
> > the
> > > > antenna will be received equally well by the sloping termination of
> the
> > > > antenna or a vertical termination wire. BUT, the sloping
termination
> > > > continues the characteristic of the Beverage antenna, in that it
> > > > predominantly responds to signals in the plane of the axis of the
> > antenna.
> > > >
> > > > The vertical termination wire allows vertically polarized signals
from
> > ALL
> > > > directions to degrade the performance of the Beverage antenna. I
> > disagree
> > > > that the quantity of signal induced in this manner is not
detrimental
> to
> > > > performance. All you have to do is insert a short piece of wire
into
> > the
> > > > antenna jack of your receiver to know how much signal that short
piece
> > can
> > > > deliver.
> > > >
> > > > I believe that small amount of signal from unwanted directions can,
in
> > > many
> > > > instances, totally obsure a weak signal from the desired direction.
> > > >
> > > > Comments?
> > > >
> > > > Milt, N5IA
> > >
> > >
> > > _______________________________________________
> > > Topband mailing list
> > > Topband@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/topband
> > >
> >
> >
>
>
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