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
On 9/4/2021 6:32 PM, Lux, Jim wrote:
On 9/4/21 6:02 PM, Stan Stockton wrote:
I’m missing something. How do I get 180 out of 2 * 900/80?
Thanks, Jim.
Stan
Sent from my iPhone
You're right.. brain freeze. But 22.5 meters seems awfully close. 2
D^2/lambda is the equation - 2 * 30*30/80 = 1800/80 = 22.5 meters
Granted that's for "directive antennas" - Something weird (maybe it's invalid
for antennas that are "smaller than a wavelength") -
On Sep 4, 2021, at 7:30 PM, Stan Stockton <wa5rtg@gmail.com> wrote:
Sent from my iPhone
Begin forwarded message:
From: "Lux, Jim" <jim@luxfamily.com>
Date: September 4, 2021 at 5:58:44 PM CDT
To: TowerTalk@contesting.com
Subject: Re: [TowerTalk] Field Strength comparison
On 9/4/21 3:36 PM, Stan Stockton wrote:
How far away (minimum) should a receive antenna be located if you wanted
to accurately measure the difference between a couple of vertical arrays -
let’s say, for example a 4 Square and a single vertical.
Thanks… Stan, K5GO
The traditional guide line for antenna ranges is 2 D^2/lambda, where D is
the diameter of the antenna. That has to do with the phase difference from
a plane wave being small enough that the gain isn't significantly wrong (I
can't remember if it's 0.1 dB or what, and I'm too lazy to calculate it now).
For a 80 m foursquare, it's roughly 30 meters across (1.414 * 20m) so 2 *
900/80 = 180 meters away
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