Visit RFCafe.com Thanks for visiting RFCafe.net Thanks for visiting the RF Cafe Archives Thank you for visiting RF Cafe Thank you for visiting the RF Cafe Archives!

RF loss in air - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

tbob
 Post subject: RF loss in air
Posted: Thu Aug 25, 2005 5:56 pm 
Does anyone know the formula to calculate the RF power loss in air from a transmitting antenna to a specified distance away from the antenna? Lets say I am transmiting 100 watts into a unity gain antenna, 400MHz. What will be the power level (in watts, dB, or uV) 100 meters away.


 
  
 
Kirt Blattenberger
 Post subject: Path Loss Equations
Posted: Thu Aug 25, 2005 10:30 pm 
 
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings tbob:

Here is the path loss equation you are looking for...


...and here is a 1-way calculator for you...
https://www.rfcafe.com/references/electr ... -1-way.htm

...and here is a 2-way (radar) calculator for you...
https://www.rfcafe.com/references/electr ... -2-way.htm

_________________
- Kirt Blattenberger :smt024
RF Cafe Progenitor & Webmaster


 
   
 
IR
 Post subject:
Posted: Fri Aug 26, 2005 5:12 am 
 
Site Admin
User avatar

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello tbob,

The Frii's formula which is given in linear terms can be also calculated in dB:

Lpath=32.5+20log (F)+20log (D)-Gtx-Grx

Where:

F- frequency in MHz
D- Distance in Km

_________________
Best regards,

- IR


 
   
 
Guest
 Post subject:
Posted: Fri Aug 26, 2005 11:41 am 
Thanks to both of you for your help. I'll have to visit this forum more often.

Bob - RF Test Engineer






Posted  11/12/2012