Signal strength
From Free net encyclopedia
In telecommunications, and particularly in radio, signal strength is the measure of how strong a signal is. Typically, this is measured as voltage per square area. Higher power uses such as broadcasting use units of millivolts per square metre (mV/m²). Very low-power uses are most often in microvolts per square metre (µV/m²).
Expressed in decibels, 1 mV/m² is 0 dBm (a shortened dB(mV/m²)), or 60 dBµ (often written dBu).
- Some examples
- 100 dBµ or 100 mV/m²: blanketing interference occurs
- 60 dBµ or 1 mV/m²: the edge of a radio station's protected area
- 40 dBµ or 100 µV/m²: the minimum strength a station can be received
Cell Signal
Although the cell broadcast tower network across the U.S. (and rest of the world) is now nearly complete, there are still many areas which 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 and 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 interference of the signals from local towers in urban areas; the construction material used in some buildings (the absorption spectra of some metals causes rapid attenuation of signal strength); and large buildings such as warehouses, hospitals and factories often have no signal further than a few metres from the outside walls.
This is particular true for the networks which operate at higher frequency since the these are attenuated more rapidly by intervening obstacles and are less able to use diffraction to circumvent obstacles due to their shorter wavelength. Cell phones in the U.S. operate at around 800MHz and 1900MHz - classified as UHF and low energy microwaves respectively.
This has lead to the rapid growth in the home cellular repeater market. The more advanced models now typically include an external directional antenna and an amplifier (usually operating at 55db 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).