Saturday, 12 March 2011
How cell phone towers work and how it affects you?
When you make a call on your mobile phone, it emits electromagnetic radio waves also known as radio frequency, or RF energy. Antenna from the nearest cell phone tower will then receive these radio waves.
Cell phone tower consists of antennas that both transmit and receive signals from mobile phones.
After receiving signal from a mobile phone, the cell phone tower then transmits the signals to a "switching center" - a telephone exchange for mobile phones. Here the call is connected either to another mobile phone or to telephone network.
A mobile phone system requires a number of cell phone towers. Each cell phone tower sits in the middle of a geographical area known as "cell". That is why mobile phones are also known as "cellular" phones.
The number of calls (or "traffic") that a cell phone tower can handle at any one time is limited by engineering design constraints. In order to operate the mobile phone network as efficiently as possible, cell phone towers are located to maximize the number of calls that can be connected during peak use periods.
Therefore, geographic size of a cell depends on the traffic during these periods. Cells in populated areas with many mobile phone users will be smaller than cells in less populated areas.
As you cross the boundary of one cell, the cell next to it will automatically take over. This is called a "hand-over" or "hand-on". It is controlled by a computer in switching center. The switching center knows which cell your mobile is in and switches it to the next cell if you move across a boundary.
Your call will continue to get "handed-on" to each cell in turn until you reach the edge of the last boundary. Then you will be out of range of any cells and your call won't be transmitted.
Almost all mobile phones, except for satellite phones, use cellular technology including GSM, CDMA (Code Division Multiple Access) and the old analog mobile phone systems.
Wireless communication systems operate at several frequencies in electromagnetic spectrum. In the US, mobile phones operate in 2 main electromagnetic frequency ranges. The older systems operate near 850 MHz and the newer personal communications services, or PCS, operate near 1900 MHz.
European mobile phones use Global System for Mobile Communications (GSM), a different technology that operates at slightly different frequencies, near 900 MHz and 1800 MHz.
Many other applications transmit energy in nearby frequency bands.
The next generation of mobile phone technology, expected to result in widespread use of videophones and access to multimedia information, is called Universal Mobile Telecommunication System (UMTS), which operates in the 2 GHz region in the UK.
The electromagnetic fields caused by mobile phones are more complex than for other electrical or electronic gadgets.
Digital mobile phones use a frequency of about 900 mega Hertz (MHz) for the GSM system and 1,800 MHz for the PCN (Personal Communication Network) system. Both fall in the microwave region of electromagnetic spectrum.
Mobile phones thus emit microwaves during transmission. Highest energy output comes during the first several seconds. A handset typically radiates 1-2 Watts energy at peak.
When you talk on your mobile phone, your voice is transmitted from the antenna as radio frequency radiation between 800 MHz and 1,800 MHz, a range that's right in the middle of microwave territory.
But a handset that is in operation also has a low-frequency magnetic field (EMF) associated not with the emitted microwaves, but with surges of electric current from the battery.
This is necessary to implement "time division multiple access" or TDMA, the system currently used to increase the number of people who can simultaneously communicate with a cell phone tower. This radiation is at 217 Hz.
With handsets that have an energy saving discontinuous transmission mode (DTX), there is an even lower frequency pulsing at 2Hz, which occurs when the user is listening, but not speaking.
The above does not include the energy fields from the cell phone tower. A cell phone tower antenna typically radiates 60 W.
Every communication between handset and cell phone tower is grouped into "frames", which are in turn grouped into "multi frames". This results in an additional low-frequency pulsing of the signal at 8.34 Hz.
This pulsing, unlike the 217 Hz radiation, is unaffected by call density. Thus it is a permanent feature of the emission.
It has been reported that the DTX pulse frequency at 2 Hz and the TDMA frequency of 8.34 Hz correspond to frequencies of electrical oscillations found in human brain, specifically the delta and alpha brain waves, respectively.
It is thus quite possible that living organisms have a 2-fold sensitivity to pulsed GSM signal, both to the microwave carrier and the lower frequency pulsing of TDMA and DTX signals.