Re: [TowerTalk] Field Strength comparison

["Lux, Jim" <jim@luxfamily.com>]

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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