# ERP derivation? - RF Cafe Forums

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Mr.Whatever
 Post subject: ERP derivation? Posted: Tue Sep 05, 2006 4:08 pm
 Captain

Joined: Fri Apr 07, 2006 6:10 pm

Posts: 18

I was reading the Electronics Engineers' Handbook and they have the following formula:

E = [7 * sqrt(pt)] / d

where E is the field strength in V/m, d is the distance in meters, and pt is the effective radiated power (ERP), which includes the transmitter gain with respect to a half-wave dipole.

Thanks!

Mr.Whatever
 Post subject: Posted: Wed Sep 20, 2006 11:59 pm
 Captain

Joined: Fri Apr 07, 2006 6:10 pm

Posts: 18

 I found the answer to this question after reading some more wave propagation stuff. I thought I'd share it.power: (V^2) / R = Ppower flux density: s = P / (4*pi*r^2), where pi = 3.14 and r = distancefield strength: e = sqrt (120 * pi * s) = sqrt(30 * P) / rA half-wave dipole has a 1.64 gain in its equatorial plane, therefore:e = sqrt(1.64*30*P) /r = 7*sqrt(p) / rPretty simple, but I hate it when other books try to make me memorize a formula. I prefer finding out how its derive, so I can start from "scratch" whenever I forget the formula.

Posted  11/12/2012