Enter the frequency of the radio wave and the distance between antennas into the calculator to determine the free space path loss.

Free Space Path Loss Formula

The following formula is used to calculate a free-space path loss. 

FSPL = (4*pi*d*f/c)^2
  • Where FSPL is the free space path loss
  • d is the distance between antennas (m)
  • f is the frequency of the radio wave (hz)
  • c is the speed of light 299 792 458 (m/s)

To calculate the free space path loss, multiply four times pi by the frequency times the distance, then divide by the speed of light. Take this result and square it.

Free Space Path Loss Definition

A free-space path loss is the attenuation of radio energy between the feed points of two antennas.

How to calculate free space path loss?

Example Problem #1:

First, determine the distance between antennas. In this example, the distance between the two antennas’ feed points is measured to be 3000 meters.

Next, determine the frequency of the radio waves being transmitted. In this example, the frequency of the waves is measured to be 5000hz.

Finally, calculate the path loss using the formula above:

FSPL = (4*pi*d*f/c)^2

= (4*3.14159*3000*5000/299,792,458)^2

= .39533.

FAQ

What factors can affect free space path loss besides distance and frequency?
Besides distance between antennas and frequency of the radio wave, factors such as the environment (urban areas with buildings vs. open space), weather conditions, and antenna characteristics (gain, polarization) can affect free space path loss.

Is free space path loss different from other types of signal loss?
Yes, free space path loss specifically refers to the loss of signal strength that occurs when a radio wave travels through free space. This is different from other types of signal loss such as insertion loss, power loss, and polarization loss, which can occur due to the characteristics of the transmission medium or components in the signal path.

How can one minimize free space path loss in a communication system?
To minimize free space path loss, one can use antennas with higher gain to increase signal strength, choose frequencies that are less susceptible to loss, reduce the distance between antennas when possible, and ensure the antennas are properly aligned. Additionally, using repeaters or amplifiers along the signal path can help to maintain signal strength over long distances.