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Formula to calculate field strengths?

> (Posted this here hoping more would see it) Does anyone
> know what the exact formula is to calculate the field
> strength of an FM signal, given a distance (ala what the
> calculator does at The FCC Propagations Curves page)? They
> don't seem to list what the actual formula is anywhere.
> Thanks in advance!
>
There is a formula to calculate field strength if it's within line of sight with no obstructions. However, there isn't a formula to take Earth's curvature into account.<P ID="signature">______________
17-year-old radio geek
Location: Princeton Junction, NJ
AIM: KewlDude471
WWPH 107.9 FM: http://wwph1079fm.no-ip.org</P>
 
> > (Posted this here hoping more would see it) Does anyone
> > know what the exact formula is to calculate the field
> > strength of an FM signal, given a distance (ala what the
> > calculator does at The FCC Propagations Curves page)?
> They
> > don't seem to list what the actual formula is anywhere.
> > Thanks in advance!
> >
> There is a formula to calculate field strength if it's
> within line of sight with no obstructions. However, there
> isn't a formula to take Earth's curvature into account.
>

Yeah within line of sight is fine, I don't need to take anything else into account. <P ID="signature">______________
Nick Langan
WNJL.com Radio
</P>
 
> Does anyone know what the exact formula is to calculate the
> field strength of an FM signal, given a distance
_______________

For far-field locations over paths with no obstructions and reflections, it is

E = SQRT(49.2*P)/D

where

E = field strength in volts/meter in the directions of maximum field
P = power in watts applied to a matched, 1/2-wave dipole radiator
D = distance in meters

R. Fry
http://rfry.org
 
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