Thanks for saving me all the typing ;-)
Chuck
WB2EDV
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. All
>> antennas have both horizontal and vertical beamwidth.
>> Depending on what you think is beam-tilt... one could
>> and some do say all antennas have a beam tilt and or
>> a beam width. Others combine the description...
>>
>> In the more commercial world of antennas, we now see
>> vertical omni repeater site antennas with adjustable
>> beam tilt.
>>
>> But I'm not sure if I'd say they have to be made with
>> 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 with
>> adjustable setting in some vertical omni models with
>> composite radomes.
>>
>> ... and you pay serious money for the adjustable beam
>> tilt models. If you pay attention to the specs, you'll
>> see values for the horizontal, vertitcal beam width and
>> where needed, the/any adjustable beam tilt values.
>>
>> Your results will probably vary...
>>
>> cheers,
>> skipp
>>
>>
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