[RFI] Inverse Square Law and RFI

[Cortland Richmond]

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 at comcast.net>
>   To: rfi at 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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