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be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
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Below are all of the forum threads, including all
the responses to the original posts.
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 halfwave dipole.
How was this formula derived?
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 = P
power flux density: s = P / (4*pi*r^2), where pi = 3.14 and r = distance
field strength: e = sqrt (120 * pi * s) = sqrt(30 * P) / r
A halfwave dipole has a 1.64 gain in its equatorial plane, therefore:
e = sqrt(1.64*30*P) /r = 7*sqrt(p) / r
Pretty 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
