Free space loss is the loss in power of an of an electromagnetic wave (such as a radio signal as it travels from the transmitter to the receiver) that is associated with the phenomenon of beam divergence and the inverse square law of electromagnetic radiation. It is usually included in path loss calculations, together with other transmission factors, to ensure that the power of a transmitter is suffient to send a receivable signal to a suitably sensitive receiver. Electromagnetic radiation is a propagating wave in space with electric and magnetic components. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... Antenna tower of Crystal Palace transmitter, London A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... In radio terminology, a receiver is an electronic device that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ... The beam divergence of an electromagnetic beam is the increase in beam diameter with distance from the aperture from which the beam emerges in any plane that intersects the beam axis. ... In physics, an inverse-square law is any physical law stating that some quantity is inversely proportional to the square of the distance from a point. ... Electromagnetic radiation can be conceptualized as a self propagating transverse oscillating wave of electric and magnetic fields. ... Path loss: In a communication system, the attenuation undergone by an electromagnetic wave in transit between a transmitter and a receiver. ...

As the name implies, free space loss assumes the transmitter and receiver are both located in free space and does not consider other sources of loss such as reflections, cable, connectors etc. A discussion of these losses is included in the article on Link budget. Similarly it does not take account of gains from particular antennas. In physics, free space is a concept of electromagnetic theory, corresponding roughly to the vacuum, the baseline state of the electromagnetic field, or the replacement for the electromagnetic aether. ... A link budget is the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc. ... A Yagi-Uda antenna An antenna or aerial is an electronic component designed to transmit or receive radio waves. ...

Free space power loss is proportional to the square of the distance between the transmitter and receiver and also proportional to the square of the frequency of the radio signal. Sine waves of various frequencies; the lower waves have higher frequencies than those above. ...

A particularly convenient way to express free space loss is in terms of dB. The loss can be expressed as: DB or db or dB may stand for: Database, an organized collection of data DB (car), a French automobile maker Decibel (dB), the ratio between two quantities, used in acoustics and electronics Deutsche Bahn, the major German railway company Deutsche Bank, a German bank Discovery Bay, a residential development in...

FSL(dB) = 20log₁₀(d) + 20log₁₀(f) + K

where d is the distance, f is the frequency, and K is a constant that depends on the units used and details of the radio link.

If d is measured in meters, f in Hz, and the link uses isotropic antennas, the expression becomes: An isotropic antenna is an ideal antenna that radiates power with unit gain uniformly in all directions and is often used to reference antenna gains in wireless systems. ...

FSL(dB) = 20log₁₀(d) + 20log₁₀(f) − 147.5

As an example, the FSL(dB) of a 1000 meter link operating at 1GHz using isotropic antennas is 92.5 dB.

See also

• Friis Transmission Equation
• Link budget

The Friis transmission equation is used in telecommunications engineering, and gives the power transmitted from one antenna to another under idealized conditions. ... A link budget is the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc. ...

External references

• Derivation of the dB version of the Path Loss Equation
• Propagation Models Chapter on Free Space Propagation