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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