Re: [RFI] Inverse Square Law and RFI

[Cortland Richmond <ka5s@earthlink.net>]

This is an issue we lost in the BPL fight; when radiating conductors are 
long in wavelength, the  transformation from  near to far fields occurs 
at greater distance than would be expected of a point source. Ignoring 
radiator size (in wavelengths)-- part of the equation --  can result in 
substantially lower calculated interference potential from such sources.
For 4 MHz 
(https://www.everythingrf.com/rf-calculators/antenna-near-field-distance-calculator 
) and  a 1000 meter radiating conductor:
 *
   Wavelength
   74.9481145m
 *
   Reactive Near Field Distance
   2264.70340834m
 *
   Radiating Near Field Distance
   26685.12761585m
 *
   Far Field (Greater than this distance)
   26685.12761585m


Assuming a "point source" (ONE meter radiator)...

 *
   Reactive Near Field Distance
   0.07161621m
 *
   Radiating Near Field Distance
   0.02668513m
 *
   Far Field (Greater than this distance)
   0.02668513m



Cortland Richmond
ka5s



On 6/13/18 8:14 AM, JW via RFI wrote:

> I suppose it should be mentioned, for completeness, that strictly speaking the 
> inverse square law is inapplicable to that range  of low band frequencies where 
> propagation of the signal via ground wave is taking place, as on the 160 meter band,
> de  Jim WB5WPA
>
>        From: Kenneth Goodwin <krgoodwin@comcast.net>
>   To: rfi@contesting.com
>   Sent: Tuesday, June 12, 2018 9:55 PM
>   Subject: Re: [RFI] Inverse Square Law and RFI
>     
> The inverse square law is a geometric result based on the surface area of a
> sphere that applies to an RF source radiating equally in all directions that
> is in perfect environment, e.g. deep space.  In most communication
> environments the ratio is closer to the fourth power especially in far field
> situations with all the good features of a typical RF environment -
> scattering, diffraction, reflection, blockage, etc.  Signal attenuation
> depends on other factors like frequency not just the distance from the RF
> source as stated in the inverse square law.  As Jim has indicated in his
> previous posting, in the real world it is never that simple.  Ken K5RG
>
>
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