Introduction to How Cell Phone Jammers

Cell phones are everywhere these days. According to the Cellular Telecommunications

and Internet Association, almost 195 million people in the United States had cell-phone
service in October 2005. And cell phones are even more ubiquitous in Europe.
It's great to be able to call anyone at anytime. Unfortunately, restaurants, movie
theaters, concerts, shopping malls and churches all suffer from the spread of cell
phones because not all cell-phone users know when to stop talking. Who hasn't seethed
through one side of a conversation about an incredibly personal situation as the talker
shares intimate details with his friend as well as everyone else in the area?
While most of us just grumble and move on, some people are actually going to
extremes to retaliate. Cell phones are basically handheld two-way radios. And like any
radio, the signal can be disrupted, or jammed.

Cell Phone Jamming Basics

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, 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, disrupting
the communication between the phone and the cell-phone base station in the tower.
t'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 means 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, all you need is 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 (sometimes referred to as 1.9-GHz) 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 actual 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.

A big jammer A portable jammer 

RANGE&FREQUENCY:

Most jammers only have a range of about 50 to 80 feet and will only effectively jam your
immediate surroundings. Mobile blabbermouths will just think they've hit a dead spot in
their cell phone company's coverage until they leave your jammers immediate vicinity.
Stronger jammers are available to cover larger structures like office buildings, movie
theaters and churches. They look like a miscellaneous metal boxes with wires sticking
out and are usually mounted on walls or ceilings (see image on right).

Most cell phone jammers come in 2 versions, one for Europe, North Africa and the Gulf
states GSM networks (900 & 1800) and one for the Americas & Canada (800 & 1900
mhz) networks. Make sure you get the right version for your location.

Simple Cell Phone Jammer

Inside Cell Phone Jammers:
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:
Cell-phone jammer
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.

Powersupply
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.
 Check your phone - 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.

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. The TRJ-89 jammer from Antenna System
& Supplies Inc. carries its own electrical generator and can block cellular
communications in a 5-mile (8-km) radius.
Corporations use jammers to stop corporate espionage by blocking voice transmissions
and photo transmissions from camera phones. On the more questionable end of the
legitimacy spectrum, 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 (as well as any other electronic transmissions) 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.