Cell phone jammer is device used to prevent cellular phones from receiving signal from base station. They can be used anywhere but mostly used where phone call would be disruptive. Cell phones are very useful because we are able to contact anyone at anytime but sometimes it become nuisance. Some cell phone users don’t know when to stop talking. Jammers are used at classrooms, temples, churches where silence is required. It creates a temporary “dead zone” to all cell phone traffic in their air system.
How Cell Phone Jammer works
Disrupting a cell phone is the same as jamming any other type of radio communication. A cell phone works by communicating with its service network through a cell tower or base station. Cell towers divide a city into small areas. As a cell-phone user drives down the street, the signal is handed from tower to tower.
Jamming device transmits on the same radio frequencies as the cell phone, disrupting the communication between the phone and the cell-phone base station in the tower.
It’s a called a denial-of-service attack. The jammer denies service of the radio spectrum to the cell-phone users within range of the jamming device.
Cell phone Jamming Device
Jamming devices overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each 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 are full-duplex devices, which mean they use two separate frequencies, one for talking and one for listening 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 service because it can receive only one of the frequencies.
Less complex devices block only one group of frequencies, while sophisticated jammers can block several types of networks at once to head off dual-mode or tri-mode phones that automatically switch among different network types to find an open signal. Some of the high-end devices block all frequencies at once, and others can be tuned to specific frequencies.
To jam a cell phone, you need a device that broadcasts on the correct frequencies. Although different cellular systems process signals differently, all cell-phone networks use radio signals that can be interrupted. GSM, used in digital cellular and PCS-based systems, operates in the 900-MHz and 1800-MHz bands in Europe and Asia and in the 1900-MHz band in the United States. Jammers can broadcast on any frequency and are effective against AMPS, CDMA, TDMA, GSM, PCS, DCS, iDEN and Nextel systems. Old-fashioned analog cell phones and today’s digital devices are equally susceptible to jamming.
The range of the jammer depends on its power and the local environment, which may include hills or walls of a building that block the jamming signal. Low-powered jammers block calls in a range of about 30 feet (9 m). Higher-powered units create a cell-free zone as large as a football field. Units used by law enforcement can shut down service up to 1 mile (1.6 km) from the device.
Inside Cell phone Jammers
Cell-phone jammers are very basic devices. It just has an on/off switch and a light that indicates it’s on. More complex devices have switches to activate jamming at different frequencies. Components of a jammer:
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.
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
Smaller jamming devices are battery operated. Some look like cell phone and use cell-phone batteries. Stronger devices can be plugged into a standard outlet or wired into a vehicle’s electrical system.
Cell phone Jammer Applications
Cell phone jamming devices were originally developed for law enforcement and the military to interrupt communications by criminals and terrorists.
The bombs that blew up commuter trains in Spain in March 2004, as well as blasts in Bali in October 2002 and Jakarta in August 2003, all relied on cell phones to trigger explosives. It has been widely reported that a cell-phone jammer thwarted an assassination attempt on Pakistani President Musharraf in December 2003.
When President Bush visited London in November 2004, it was reported that British police considered using jammers to protect the president’s motorcade through London.
During a hostage situation, police can control when and where a captor can make a phone call. Police can block phone calls during a drug raid so suspects can’t communicate outside the area.
Cell-phone jammers can be used in areas where radio transmissions are dangerous, (areas with a potentially explosive atmosphere), such as chemical storage facilities or grain elevators.
Corporations use jammers to stop corporate espionage by blocking voice transmissions and photo transmissions from camera phones. There are rumors that hotel chains install jammers to block guests’ cell-phone usage and force them to use in-room phones at high rates.
Cell Phone Jamming Legal Issues
In the United States, United Kingdom, Australia and many other countries, blocking cell-phone services is against the law. In the United States, cell-phone jamming is covered under the Communications Act of 1934, which prohibits people from “willfully or maliciously interfering with the radio communications of any station licensed or authorized” to operate. In fact, the “manufacture, importation, sale or offer for sale, including advertising, of devices designed to block or jam wireless transmissions is prohibited” as well.
Jamming is seen as property theft, because a private company has purchased the rights to the radio spectrum, and jamming the spectrum is akin to stealing the property the company has purchased.
The Federal Communications Commission is charged with enforcing jamming laws. However, the agency has not yet prosecuted anyone for cell-phone jamming.
In most countries, it is illegal for private citizens to jam cell-phone transmission, but some countries are allowing businesses and government organizations to install jammers in areas where cell-phone use is seen as a public nuisance.
Armenia: legal 
Australia: illegal to operate, supply or possess
Belgium: illegal to sell, possess and operate (licensed part of the spectrum).
Canada: illegal, except by federal law-enforcement agencies who have obtained approval
People’s Republic of China: Used by the Education government department as a method of thwarting cheating in schools. During major end of year exams, mobile phone jammers are used in areas surrounding high schools to prevent students inside from receiving calls or text messages, which may be used for illicit purposes. In some municipalities however, rather than the use of jammers, mobile signal towers close to schools are temporarily shut down for the duration of the week as exams are in progress.
Czech Republic: illegal.
France: France legalized cell-phone jammers in (movie) theaters and other places with performances in 2004.Abandoned due to complaints regarding emergency calls. Still legally used inside jails.
Germany: illegal, but installation in jails has been proposed.
India: Government, Religious Places, Prisons and Educational Institution use jammers.
Iran: illegal to operate for civilians but allowed for police forces and military. It is however legal to own such units, which can be bought in electronic markets without a license. In most jails, libraries and university classrooms such jammers are already in use. In the 2009-2010 Iranian election protests, police forces used cell phone and Bluetooth jammers.
Ireland: illegal to operate. Legally used inside prisons by the Irish Prison Service.
Italy: technically not illegal to own, but illegal to operate, since the Italian law specifically prohibits disturbing radio and telephoning communications.
GSM jammers are however legal to be used in places like hospitals, churches, movie theatres and other places with performances, and other buildings where and when the use of mobile telephones may result in a leak of sensitive information: on such occasions, jammers are legal as long as their operation doesn’t interfere with electronic medical equipment and allows mobile phones to make emergency calls. Tri-Band Jammers are reserved to, and in use with, the police forces and are being experimented in prisons.
Japan: Illegal to use, but legal to own. Buying of mobile short range versions is allowed. Use of fixed high output jammers with long range is illegal, with fines of up to max $250,000USD and/or 5 years in prison.
Mexico: legal inside jails, often used also in churches and hospitals.
New Zealand: legal inside jails.
Norway: illegal to own and operate. The police and the military can use jammers in situations in which it is necessary.
Pakistan: legal inside banks, often used also in libraries.
Turkey: illegal. Only the police and the military use jammers.
Ukraine: legal, planned to be used in schools
United Kingdom: illegal to use, but legal to own. Installation in jails has been proposed
United States: Cell phone blocking devices are used by federal officials under certain circumstances. Privacy rights of property owners may affect the policy and application of law within buildings. The FCC may issue a permit that waivers the law for private use.
Alternatives to Cell Phone Jamming
While the law clearly prohibits using a device to actively disrupt a cell-phone signal, there are no rules against “passive cell-phone blocking”. That means using things like wallpaper or building materials embedded with metal fragments to prevent cell-phone signals from reaching inside or outside the room. Some buildings have designs that block radio signals by accident due to thick concrete walls or a steel skeleton.
Companies are working on devices that control a cell phone but do not “jam the signal.” One device sends incoming calls to voicemail and blocks outgoing calls. The argument is that the phone still works, so it is technically not being jammed. It is a legal gray area that has not been ruled on by the FCC as of April 2005.
Cell-phone alerts are available that indicate the presence of a cell-phone signal. These have been used in hospitals where cell-phone signals could interfere with sensitive medical equipment. When a signal is detected, users are asked to turn off their phones.
Cell-phone users don’t know they’re being jammed. The phones just indicate that there’s no service or no signal from the network. The jammer simply interrupts the phone’s ability to establish a link with the nearest cell-phone tower. If the battery on your phone is okay, and you’d like to continue your conversation, try walking away from the area. You may be able to get out of the jammer’s range with just a few steps.
Every technology has good aspect as well as bad aspect the important thing is, how we are using it.
There are some bad aspects of mobile Jammers like,
Jamming blocks all calls in the area, not just the annoying ones.
Jamming a signal could block the call of a babysitter frantically trying to contact a parent or someone trying to call for an ambulance.
Cell Phone Jammers are very useful to society from the antisocial elements.
We can save our national leaders.
We can restrict the communication network between the anti social elements.
Cell phone Jammers prevent the students from carrying cell phones to the college.
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