Cell phone jammer

A cell phone jammer is an instrument used to prevent cellular phones from receiving signals from base stations. When used, the jammer effectively disables cellular phones. These devices can be used in practically any location, but are found primarily in places where a phone call would be particularly disruptive because silence is expected.


As with other radio jamming, cell phone jammers block cell phone use by sending out radio waves along the same frequencies that cellular phones use. This causes enough interference with the communication between cell phones and towers to render the phones unusable. On most retail phones, the network would simply appear out of range. Most cell phones use different bands to send and receive communications from towers (called frequency division duplexing, FDD). Jammers can work by either disrupting phone to tower frequencies or tower to phone frequencies. Smaller handheld models block all bands from 800 MHz to 1900 MHz within a 30-foot range (9 meters). Small devices tend to use the former method, while larger more expensive models may interfere directly with the tower. The radius of cell phone jammers can range from a dozen feet for pocket models to kilometers for more dedicated units. The TRJ-89 jammer can block cellular communications for a 5-mile (8 km) radius.


Less energy is required to disrupt signal from tower to mobile phone, than the signal from mobile phone to the tower (also called base station), because the base station is located at larger distance from the jammer than the mobile phone and that is why the signal from the tower is not as strong.


Older jammers sometimes were limited to working on phones using only analog or older digital mobile phone standards. Newer models such as the double and triple band jammers can block all widely used systems (CDMA, iDEN, GSM, et al.) and are even very effective against newer phones which hop to different frequencies and systems when interfered with. As the dominant network technology and frequencies used for mobile phones vary worldwide, some work only in specific regions such as Europe or North America. Some Cell Phone Jammers have been introduced to some State Prisons in the United States. Cell phones that have been sneaked into prison pose a security risk for guards and property owners living near by.

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.
The jammer's effect can vary widely based on factors such as proximity to towers, indoor & outdoor settings, presence of buildings and landscape, even temperature and humidity play a role.
There are concerns that crudely designed jammers may disrupt the functioning of medical devices such as pacemakers.However, like cellphones, most of the devices in common use operate at low enough power output (<1W) to avoid causing any problems.

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