[TowerTalk] Field Strength comparison

[Wes]

On 9/4/2021 8:19 PM, Lux, Jim wrote:
> On 9/4/21 8:05 PM, Wes wrote:
>> For an illustration try this: 
>> http://www.cuminglehman.com/wp-content/uploads/Introduction_to_Antenna_Test_Ranges_Measurements_Instrumentation.pdf
>>
>> and look at the figure on  page 4.  This shows the usual antenna range 
>> situation where the test antenna is receiving a signal from a point, or small 
>> aperture source.  This is how I would run this comparison.  I think, but do 
>> not know for sure, that I would use the larger dimension of the vertical(s) 
>> as the "D" in the equation.  The idea is to have a plane, or near plane, wave 
>> over the whole aperture of the test antenna in both directions. Note that 
>> some antennas, Yagis for instance, can have an effective aperture larger that 
>> the physical aperture.
>>
>> Wes  N7WS 
>
>
> But that's the 2D^2/lambda  - and that comes out strangely small.   And it's 
> not effective aperture (that's more about voltage/power at the feed) - this is 
> about the physical optics.
>
> D =30m (across the 4 square diagonally) is almost certainly bigger than the 
> height of the 80m elements (20m?)

Sure, that's what I said.  There are two test cases, 1) a single vertical and 2) 
four verticals.  The four verticals may, or may not, have 1/4 lambda spacing and 
they could be shortened, loaded antennas.  Pick the largest physical dimension.

Wes N7WS