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# RF loss in air - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would 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. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

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

 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.

 Post subject: Path Loss Equations Posted: Thu Aug 25, 2005 10:30 pm

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...
http://www.rfcafe.com/references/electr ... -1-way.htm

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

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- Kirt Blattenberger
RF Cafe Progenitor & Webmaster

 Post subject: Posted: Fri Aug 26, 2005 5:12 am

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

 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
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