radio transmission Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...

, transmitter power output (TPO) is the actual amount of

power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...

(in

watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...

s) of

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the ...

(RF) energy that a

transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...

produces at its output. This is not the amount of power that a

radio station Radio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based radi ...

reports as its power, as in "we're 100,000 watts of rock 'n' roll", which is usually the

effective radiated power Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter. It is the total power in watts that would h ...

(ERP). The ERP for VHF-/UHF-transmitters is normally more than the TPO, for LF-/MF-transmitters it has nearly the same value, while for VLF-transmitters it may be less.

Signal formula

The

radio antenna In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an ...

's design "focuses" the

signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...

toward the horizon, creating gain and increasing the ERP. There is also some loss (negative gain) from the

feedline In a radio antenna (radio), antenna, the feed line (feedline), or feeder, is the cable or other transmission line that connects the antenna with the radio transmitter or Radio receiver, receiver. In a transmitting antenna, it feeds the radio ...

, which reduces some of the TPO to the antenna by both resistance and by

radiating In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visib ...

a small part of the signal. The basic equation relating transmitter to effective power is: ::

TPO\ \times\ loss_\ \times\ gain_\ =\ ERP

Note that in this formula the Antenna Gain is expressed with reference to a tuned dipole ( dBd)

Signal formula

References

See also