I agree with Kevin and have used this in the
commercial field where the anteena was originallt cut
higher than was to be used.
I mounted the antenna upside-down and had good
results-with some noticed downtilt which was good for
the application .On the same token keep in mind that
most of the efficiency of the collinear design lies at
the first radiating element - reduced radiation as one
extends to the end of the antenna.
Bradley glen zs5swt /zs5wt
--- Chuck Kelsey <[EMAIL PROTECTED]> wrote:
> Thanks for saving me all the typing ;-)
> Kevin Custer wrote:
> > I think what Chuck was getting at was the
> 'automatic' beamtilt of a
> > vertical omni collinear (usually fiberglass) when
> it is run outside of
> > its specified bandwidth. As a function of the
> element length in a
> > coaxial collinear as compared to the applied
> frequency, the vertical
> > beam pattern will change with applied frequency.
> If a coaxial collinear
> > is fed with a signal that is exactly on its design
> frequency, the
> > vertical beam pattern will be centered about the
> antenna, and the
> > antenna will be at its highest radiating
> efficiency. If a coaxial
> > collinear is fed with a signal that is 2% lower
> than its design, the
> > antenna will exhibit a vertical beam downtilt of
> approximately 3 degrees
> > and suffer approximately 10% loss in overall gain.
> If a signal that is
> > 2% higher than the antenna design is fed into a
> coaxial collinear,
> > vertical beam uptilt of approximately 3 degrees
> will occur, and again a
> > loss of overall gain.
> > These instances are not the case with binary or
> corporate fed dipole
> > arrays, as the phasing harness predominantly
> controls the vertical beam
> > pattern. Beam Tilt and efficiency doesn't change
> very much with applied
> > frequency, and is one reason that the exposed
> dipole array is a better
> > choice where wide band operation is required.
> > Kevin Custer
> > skipp025 wrote:
> >> Kind of loaded question/statement/answer really.
> >> antennas have both horizontal and vertical
> >> Depending on what you think is beam-tilt... one
> >> and some do say all antennas have a beam tilt and
> >> a beam width. Others combine the description...
> >> In the more commercial world of antennas, we now
> >> vertical omni repeater site antennas with
> >> beam tilt.
> >> But I'm not sure if I'd say they have to be made
> >> fiberglass radomes (covers). There's more than
> one method
> >> used by the various mfgrs to adjust the beam tilt
> - beam
> >> width. For the most part we only see some models
> >> adjustable setting in some vertical omni models
> >> composite radomes.
> >> ... and you pay serious money for the adjustable
> >> tilt models. If you pay attention to the specs,
> >> see values for the horizontal, vertitcal beam
> width and
> >> where needed, the/any adjustable beam tilt
> >> Your results will probably vary...
> >> cheers,
> >> skipp
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