- Return loss
In telecommunications, return loss or reflection loss is the loss of signal power resulting from the reflection caused at a discontinuity in a transmission line or optical fiber. This discontinuity can be a mismatch with the terminating load or with a device inserted in the line. It is usually expressed as a ratio in decibels (dB);
- where RL(dB) is the return loss in dB, Pi is the incident power and Pr is the reflected power.
Two lines or devices are well matched if the return loss is high. A high return loss is therefore desirable as it results in a lower insertion loss. Return loss may be given a minus sign, see below.
Properly, loss quantities, when expressed in decibels, should be positive numbers.[note 1] However, return loss has historically been expressed as a negative number, and this convention is still widely found in the literature.
Taking the ratio of reflected to incident power results in a negative sign for return loss;
- where RL'(dB) is the negative of RL(dB).
Caution is required when discussing increasing or decreasing return loss since these terms strictly have the opposite meaning when return loss is defined as a negative quantity.
In metallic conductor systems, reflections of a signal traveling down a conductor can occur at a discontinuity or impedance mismatch. The ratio of the amplitude of the reflected wave Vr to the amplitude of the incident wave Vi is known as the reflection coefficient Γ.
When the source and load impedances are known values, the reflection coefficient is given by
Return loss is the negative of the magnitude of the reflection coefficient in dB. Since power is proportional to the square of the voltage, return loss is given by,
where the vertical bars indicate magnitude. Thus, a large positive return loss indicates the reflected power is small relative to the incident power, which indicates good impedance match from source to load.
When the actual transmitted (incident) power and the reflected power are known (i.e. through measurements and/or calculations), then the return loss in dB can be calculated as the difference between the incident power Pi (in dBm) and the reflected power Pr (in dBm),
In an optical fiber, the loss that takes place at any discontinuity of refractive index, especially at an air-glass interface such as a fiber endface, at which a fraction of the optical signal is reflected back toward the source. This reflection phenomenon is also called "Fresnel reflection loss," or simply "Fresnel loss."
Fiber optic transmission systems use lasers to transmit signals over optical fiber, and a high optical return loss (ORL) can cause the laser to stop transmitting correctly. The measurement of ORL is becoming more important in the characterization of optical networks as the use of wavelength-division multiplexing increases. These systems use lasers that have a lower tolerance for ORL, and introduce elements into the network that are located in close proximity to the laser.
where is the reflected power and is the incident, or input, power.
- Hybrid balance
- Insertion loss
- Signal reflection
- Standing wave ratio
- Time-domain reflectometer
- Optical time domain reflectometer
- Mismatch loss
- ^ Trevor S. Bird, "Definition and Misuse of Return Loss", IEEE Antennas & Propagation Magazine, vol.51, iss.2, pp.166-167, April 2009.
- ^ Noel G. Barton, Jacques Periaux, "Coupling of fluids, structures, and waves in aeronautics", proceedings of a French-Australian workshop in Melbourne, Australia, 3–6 December 2001, p.187, Springer, 2003 ISBN 3540402225.
- Federal Standard 1037C and from MIL-STD-188
- Optical Return Loss Testing—Ensuring High-Quality Transmission EXFO Application note #044
Wikimedia Foundation. 2010.
Look at other dictionaries:
Return loss — A&V A measure of the accuracy of the impedance match between a signal source (such as a cable) and its terminating load. An unequal impedance match causes some of the power from the source to be reflected back to the source, resulting in signal… … Audio and video glossary
Balance return loss — In telecommunications, balance return loss is one of two things: * A measure of the degree of balance between two impedances connected to two conjugate sides of a hybrid set, coil, network, or junction. * A measure of the effectiveness with which … Wikipedia
Output return loss — A&V A measure of the accuracy of the impedance match between a signal source (such as a cable) and its terminating load. An unequal impedance match causes some of the power from the source to be reflected back to the source, resulting in signal… … Audio and video glossary
echo return loss — (ERL) The attenuation of echo currents in one direction caused by telephone circuits in the other direction … IT glossary of terms, acronyms and abbreviations
Loss — may refer to:*A negative difference between retail price and cost of production *An event in which the team or individual in question did not win. *Loss (baseball), a pitching statistic in baseball *Attenuation, a reduction in amplitude and… … Wikipedia
Return On AC Power Loss — ist eine BIOS Option IBM kompatibler Personal Computer (PC) Alternative Bezeichnungen Je nach BIOS und Motherboard Hersteller sind u. a. folgenden Bezeichnungen gebräuchlich: Restore On AC Power Loss AC (Auto) Power Recovery AC Power On After… … Deutsch Wikipedia
Return — may refer to:* Return (architecture), the receding edge of a flat face * Return (finance), the financial term for the profit or loss derived from an investment * Tax return, a form submitted to taxation authorities * Carriage return, a key on an… … Wikipedia
Return — The gain or loss of a security in a particular period. The return consists of the income and the capital gains relative on an investment. It is usually quoted as a percentage. The general rule is that the more risk you take, the greater the… … Investment dictionary
Loss and Gain — Infobox Book | name = Loss and Gain image caption = Title Page, 8th Ed., 1881 author = John Henry Newman country = England language = English genre = Philosophical novel, Campus novel publisher = Burns Oates pub date = 1848 Loss and Gain is a… … Wikipedia
Return to Oz — Infobox Film name = Return to Oz caption = Theatrical release poster director = Walter Murch producer = Paul Maslansky writer = L. Frank Baum (novels) Gill Dennis Walter Murch starring = Fairuza Balk Nicol Williamson Jean Marsh Piper Laurie Matt… … Wikipedia