ERP derivation?  RF Cafe Forums

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







Copyright: 1996 
2024 Webmaster:
Kirt Blattenberger,
BSEE  KB3UON 
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dialup modems blazed along at 14.4 kbps
while typing up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website: AirplanesAndRockets.com

