# Forum

## Free space path loss

3 posts by 2 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: February 18, 2006:
• hi all,
i was going through the connect802 website where i found this formula

dBLoss = 96.6 + 20 Log10 (distance in miles) + 20 Log10 (frequency in GHz)

This one contradicts the formula given on pg no.97 in the CWNA official guide V3.
Can anyone help me out here.

Thnx,
Hardik.

The paragraph is here below.

"The Friis Free Space Equation (in decibel form) is commonly presented as the way to determine signal loss through the air between two points. This model calculates signal strength based on the spherical expansion of the propagating wave front. As the "sphere" gets bigger, the surface increases, and, consequently, the density of the propagating signal energy decreases. The Friis equation is the most widely employed formula for calculating path loss and is often seen written in a form similar to the following:

dBLoss = 96.6 + 20 Log10 (distance in miles) + 20 Log10 (frequency in GHz)

You may see this equation presented with a different "constant of proportionality" (the "96.6" value) when the units (miles, GHz) are different. Of course, for a design involving obstructions, building interiors, or specific noise or interference sources, the Connect802 Suite Spot Predictive Site Survey, employing RF modeling and simulation software, provides a design that incorporates a more complete picture of the wireless network installation location. Unfortunately, the Friis equation only presents part of the story for practical transmission system design. Many factors, beyond simple spherical expansion, come into play to effect the strength of a transmitted signal.

The relationship between theoretical calculations of path loss and the actual path loss experienced in the real-world has been the subject of many research projects and technical papers. A number of mathematical formulas have been developed to estimate link performance based on the type
of link being designed (urban versus suburban areas, smooth versus rough terrain, atmospheric conditions, etc."

• GHz compared to MHz, my man.

• hey man...
that almost disappeared in front of my eyes i guess...
anywys thanx ..
Hardik.

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