Hold on there Bradley...

An antenna that is built for a higher frequency than what you are inputting will exhibit downtilt in its original orientation.


bradley glen wrote:
Hi All

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.

Good luck
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... 



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