26-11-2012, 06:33 PM
cell phone jammer
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INTRODUCTION
A GSM Jammer is a device that transmit signal on the same frequency at which the GSMsystem operates, the jamming success when the mobile phones in the area where the jammer islocated are disabled.Communication jamming devices were first developed and used by military. Wheretactical commanders use RF communications to exercise control of their forces, an enemy hasinterest in those communications. This interest comes from the fundamental area of denying thesuccessful transport of the information from the sender to the receiver.
Nowadays the mobile jammer devices are becoming civilian products rather thanelectronic warfare devices, since with the increasing number of the mobile phone users the needto disable mobile phones in specific places where the ringing of cell phone would be disruptivehas increased. These places include worship places, university lecture rooms, libraries, concerthalls, meeting rooms, and other places where silence is appreciated
History
The rapid proliferation of cell phones at the beginning of the 21st century to near ubiquitous status eventually raised problems, such as their potential use to invade privacy or contribute to academic cheating. In addition, public backlash was growing against the disruption cell phones introduced in daily life. While older analog cell phones often suffered from poor reception and could even be disconnected by simple interference such as high frequency noise, increasingly sophisticated digital phones have led to more elaborate counters. Cell phone jamming devices are an alternative to more expensive measures against cell phones, such as Faraday cages, which are mostly suitable as built in protection for structures. They were originally developed for law enforcement and the military to interrupt communications by criminals and terrorists. Some were also designed to foil the use of certain remotely detonated explosives. The civilian applications were apparent, so over time many companies originally contracted to design jammers for government use switched over to sell these devices to private entities. Since then, there has been a slow but steady increase in their purchase and use, especially in major metropolitan areas.
OPERATION
Jamming devices overpower the cell phone by transmitting a signal on the samefrequency as the cell phone and at a high enough power that the two signals collide and canceleach other out. Cell phones are designed to add power if they experience low-level interference,so the jammer must recognize and match the power increase from the phone. Cell phones arefull-duplex devices, which mean they use two separate frequencies, one for talking and one forlistening simultaneously. Some jammers block only one of the frequencies used by cell phones,which has the effect of blocking both. The phone is tricked into thinking there is no servicebecause it can receive only one of the frequencies. Less complex devices block only one groupof frequencies, while sophisticated jammers can block several types of networks at once to headoff dual-mode or tri-mode phones that automatically switch among different network types tofind an open signal. Some of the high-end devices block all frequencies at once and others can betuned to specific frequencies.
To jam a cell phone, all you need is a device that broadcasts on the correct frequencies. Oldfashionedanalog cell phones and today's digital devices are equally susceptible to jamming.Disrupting a cell phone is the same as jamming any other type of radio communication. A cellphone works by communicating with its service network through a cell tower or base station.Cell towers divide a city into small areas, or cells. As a cell phone user drives down the street,the signal is handed from tower to tower.A jamming device transmits on the same radio frequencies as the cell phone, disruptingthe communication between the phone and the cell-phone base station in the town.It's a called a denial-of
service attack. The jammer denies service of the radio spectrumto the cell-phone users within range of the jamming device. Older jammers sometimes werelimited to working on phones using only analog or older digital mobile phone standards. Newermodels such as the double and triple band jammers can block all widely used systems and are even very effective against newer phones which hop to differentfrequencies and systems when interfered with. The power of the jammer's effect can vary widely based on factors such as proximity totowers, indoor and outdoor settings, presence of buildings and landscape, even temperature and humidity play a role.
Components of a jammer include:
Antenna:
Every jamming device has an antenna to send the signal. Some are contained within an electrical cabinet. On stronger devices, antennas are external to provide longer range and may be tuned for individual frequencies. Some devices can store the frequencies that they have jammed to prevent later tuning necessary in repeated use of that frequency.
Circuitry:
The main electronic components of a jammer are:
Voltage-controlled oscillator — Generates the radio signal that will interfere with the cell phone signal
Tuning circuit — Controls the frequency at which the jammer broadcasts its signal by sending a particular voltage to the oscillator
Noise generator — Produces random electronic output in a specified frequency range to jam the cell-phone network signal (part of the tuning circuit)
RF amplification (gain stage) — Boosts the power of the radio frequency output to high enough levels to jam a signal
Power supply:
Smaller jamming devices are battery operated. Some look like cellphones and use cellphone batteries. Stronger devices can be plugged into a standard outlet or wired into a vehicle's electrical system.