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 (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 up ...

(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 radio ...

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's design "focuses" the signal toward the

horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...

, creating

gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in de ...

and increasing the ERP. There is also some loss (negative gain) from the

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

, which reduces some of the TPO to the antenna by both resistance and by radiating a small part of the signal. The basic

equation In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in F ...

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