A Radio Frequency (RF) Jammer is a device used to disrupt or prevent communication via a broadcasted RF signal. Cell phone jammers work by creating a “dead zone” in the immediate vicinity of the device, which temporarily blocks the signals that make cell phone transmission possible. Most commercially marketed cell phone jammers are small enough to fit in the palm of a hand or in a pocket. The tradeoff is that their range is limited to an average 50 to 80 feet. Larger and more powerful cell phone jammers have a range that can be measured in miles. Read more to know how is jamming done and components used to make a jammer.

Cell phones work by communicating with a service network through the utilization of cellular towers or base stations. Individual towers partition cities into small sections called cells. As a cell phone user traverses the cells in an area, the signal is passed from tower to tower. The jammer works by broadcasting a white noise signal or a wave bubble..

Jamming devices take advantage of this fact by transmitting on the spectrum of radio frequencies used by cellular devices. Through its concurrent transmission, the jamming device is able to disrupt the two-way communication between the phone and the base station. This form of a denial-of-service attack inhibits all cellular communication within range of the device. Disrupting a cell phone is the same as jamming any other type of radio communication.

HOW IS JAMMING DONE??

Through the transmission of a high power signal on the same frequency of a cell phone, the jamming device creates a competing signal that collides with, and, in effect, cancels out the cellular signal. Cell phones, which are designed to increase power in the case of low levels of interference, react to this interference. Consequently, jamming devices must be aware of any increases in power by the cellular device and match that power level accordingly.

As cellular telephones are full-duplex devices utilizing two separate frequencies (one for talking, one for listening, where all parties to a call can talk at the same time as opposed to half-duplex walkie-talkies and CBs), any removal of one of these frequencies tricks the phone into thinking there is no cellular service. Consequently, the jammer need only block one of the frequencies.

The less complex jammers can only block a specific frequency group while the more complex jammers can block several different networks thus preventing dual- or tri-mode phones from switching to a different network with an open signal. Jammers are able to broadcast on any frequency and can interrupt AMPS, CDMA, TDMA, GSM, PCS, DCS, iDEN and Nextel systems. The effective range of a jammer is dependent upon the strength of its power source and the immediate physical environment (hills or walls which may block the jamming signal). Lower powered jammers have a call-block range of about 30 feet while higher power units can create a cellular signal-free zone about the size of a football field. In addition, certain units applied by law enforcement have been known to shut down cellular service approximately 1 mile from the jamming device.

BASIC COMPONENTS IN A JAMMER

Electronically speaking, cell-phone jammers are very basic devices. The simplest just have 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 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.

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 cell phone and use cell-phone batteries. Stronger devices can be plugged into a standard outlet or wired into a vehicle’s electrical system.

Sorce:forensicswiki.org,howstuffworks.com

Posted By

Sumanth