- Signal strength
telecommunications, particularly in radio, signal strength refers to the magnitude of the electric fieldat a reference point that is a significant distance from the transmitting antenna. It may also be referred to as received signal level or field strength. Typically, it is expressed in voltageper lengthor signal power received by a reference antenna. High-powered transmissions, such as those used in broadcasting, are expressed in dB- millivolts per metre(dBmV/m). For very low-power systems, such as mobile phones, signal strength is usually expressed in dB- microvolts per metre (dBµV/m) or in decibels above a reference level of one milliwatt (dBm). In broadcasting terminology, 1 mV/m is 1000 µV/m or 60 dBµ (often written dBu).
*100 dBµ or 100 mV/m:
blanketing interferencemay occur on some receivers
*60 dBµ or 1.0 mV/m: frequently considered the edge of a
radio station's protected area in North America
*40 dBµ or 0.1 mV/m: the minimum strength at which a station can be received with acceptable quality on most receivers
Relationship to Average Radiated Power
The electric field strength at a specific point can be determined from the power delivered to the transmitting antenna, its geometry and radiation resistance. Consider the case of a center-fed half-wave
dipole antennain free space(). If constructed from thin conductors, the current distribution is essentially sinusoidal and the radiating electric field is given by
where is the angle between the antenna axis and the vector to the observation point, is the peak current at the feed-point, is the permittivity of free-space, is the speed of light in a vacuum, and is the distance to the antenna in meters. When the antenna is viewed broadside () the electric field is maximum and given by :
Solving this formula for the peak current yields
The average power to the antenna is
where is the center-fed half-wave antenna’s radiation resistance. Substituting the formula for into the one for and solving for the maximum electric field yields
Therefore, if the average power to a half-wave dipole antenna is 1 mW, then the maximum electric field at 313 m (1027 ft) is 1 mV/m (60 dBµ).
For a short dipole () the current distribution is nearly triangular. In this case, the electric field and radiation resistance are
Using a procedure similar to that above, the maximum electric field for a center-fed short dipole is
It must be emphasized that the formulas above are illustrative and only apply when there are no conductive objects near the antenna and observation point and when the path between the two is unobstructed. Consequently, they might not provide accurate estimates of signal strength for radio transmitters in environments where signals are scattered and absorbed by buildings, the terrain and vegetation.
Although there are cell phone base station tower networks across many nations globally, there are still many areas within those nations that do not have good reception. Some rural areas are unlikely ever to be effectively covered since the cost of erecting a cell tower is too high for only a few customers. Even in high reception areas it is often found that basements and the interiors of large buildings have poor reception.
Weak signal strength can also be caused by
destructive interferenceof the signals from local towers in urban areas, or by the construction materials used in some buildings causing rapid attenuation of signal strength. Large buildings such as warehouses, hospitals and factories often have no usable signal further than a few metres from the outside walls.
This is particularly true for the networks which operate at higher
frequencysince these are attenuated more rapidly by intervening obstacles, although they are able to use reflectionand diffractionto circumvent obstacles.
Cell phones in the U.S. operate at around 800 MHz and PCS phones at 1900 MHz, classified as
UHFand low energy microwavesrespectively. This has led to the rapid growth in the home cellular repeatermarket. The more advanced models now typically include an external directional antennaand an amplifier (usually operating at 55 dB gain), which is generally enough to turn a very weak signal into a clear one over the local area (from around a thousand square feet to over twenty thousand).
Dead zone (cell phone)
* [http://www.signalmap.com Cell Phone Signal Strength Map]
* [http://www.wi-ex.com Wi-Ex: Extending Cell Zones]
Wikimedia Foundation. 2010.
Look at other dictionaries:
signal strength — In radio, a measure of the received radio frequency power, generally expressed in decibels relative to some standard value. Normally, it is either 1 milliwatt or that power which would have resulted at the same distance under free space… … Aviation dictionary
Received Signal Strength Indication — In telecommunications, Received Signal Strength Indication (RSSI) is a measurement of the power present in a received radio signal.RSSI is generic radio receiver technology metric, which is usually invisible to the userof device containing the… … Wikipedia
Received Signal Strength Indication — En télécommunications, le Received Signal Strength Indication ou RSSI est une sortie d un système de réception d un signal sans fil (classiquement un signal radio). Son utilité est de fournir un signal lié à l intensité du signal reçu. Ainsi, la… … Wikipédia en Français
sound signal strength variation — garsinio signalo lygio kitimas statusas T sritis radioelektronika atitikmenys: angl. sound signal strength variation vok. Lautstärkeränderung, f; Lautstärkeschwankung, f rus. изменение уровня звукового сигнала, n pranc. variation d intensité du… … Radioelektronikos terminų žodynas
Received Signal Strength Indication — Die Received Signal Strength Indication (RSSI) stellt einen Indikator für die Empfangsfeldstärke kabelloser Kommunikationsanwendungen dar. Dieser Indikator wird von Mobiltelefonen und anderen auf Funkkommunikation angewiesenen Systemen benötigt,… … Deutsch Wikipedia
Received Signal Strength Indication — RSSI (англ. Received Signal Strength Indication) в телекоммуникации, устройство для измерения уровня мощности принимаемого сигнала. Простейшие схемы разрабатываются, чтобы принять входящий сигнал и сформировать аналоговое выходное… … Википедия
strength — [streŋθ, strenθ] noun [countable] 1. FINANCE ECONOMICS the value of a country s money, especially when this is at a high level: strength of • the strength of the yen on the international money markets 2. the p … Financial and business terms
Strength — is the amount of force that a muscle or group of muscles can exert.Strength may refer to:Physical ability: *Physical strength, as in people or animals *Superhuman strength, as in fictional characters *a character attribute (role playing… … Wikipedia
strength — noun 1 how strong sb/sth is ADJECTIVE ▪ considerable, enormous, great, immense, incredible, tremendous ▪ high ▪ The material has exceptionally high … Collocations dictionary
signal-to-noise ratio — TV (S/N) Relationship between signal strength and a medium s inherent noise. VideoS/N indicates how grainy or snowy a picture will be, plus its color accuracy; audio S/N specifies amount of background tape hiss present with low or no volume… … Audio and video glossary