In telecommunication

Telecommunication

Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

, relative transmission level is the ratio of the signal power

Power (physics)

In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...

, at a given point in a transmission system

Transmission system

In telecommunications a transmission system is a system that transmits a signal from one place to another. The signal can be an electrical, optical or radio signal....

, to a reference signal power.

The ratio

Ratio

In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

 is usually determined by applying a standard test tone

Standard test tone

In telecommunication, a standard test tone is a single-frequency signal with a standardized level generally used for level alignment of single links and of links in tandem....

 at zero transmission level point (or applying adjusted test tone power at any other point) and measuring the gain

Gain

In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...

 or loss to the location of interest. A distinction should be made between the standard test tone power and the expected median

Median

In probability theory and statistics, a median is described as the numerical value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to...

power of the actual signal required as the basis for the design of transmission systems.