Design And Construction Of A Remote Controlled Tri–band Frequency Jammer.

2.3.4 Type “D” Device (Direct Receive & Transmit Jammers)
This jammer behaves like a small, independent and portable base stations, which can directly interact intelligently or unintelligently with the operation of the local mobile pone. The jammer is predominantly in receive mode and will intelligently chose to interact and block the cell phone directly if it is within close proximity of the jammer.
2.3.5    Type E Device (EMI Shield – Passive Jamming)
This technique is using EMI suppression techniques to make a room into what is called Faraday cage. Although labour intensive to construct, the Faraday cage essentially blocks or greatly attenuates, virtually all electromagnetic radiation from entering or leaving the cage – or in this case a target room [17].

The jammer block diagram consists of a power supply which usually provides the needed DC voltages to the other units of the circuit. An Intermediate frequency (IF) is generated by tuningthe Oscillator as desired. The RF amplifier amplifies the signal that is tuned by the tuning circuit and that generated by the noise generator and transmitted to the air via the antenna. The concept came into existence from military application in situations where countries during war situation willingly prevent their radio transmission from being intercepted by the enemy; they used RF jammers which does jamming near border areas. Cell phone jamming devices thus became the exclusive use of law enforcement agents and the military in particular to intrude on communications and transmissions by felons, terrorists and generally people on the other side of the law. The explosions of passenger trains in Spain (March 2004), and detonations in Bali (October 2002), Jakarta (August 2003) and the independence day bombing in Nigeria (October 2010), all depended on cell phones to activate the explosives. It has been commonly stated that a cell-phone jammer stopped a homicide effort on Pakistani President, Musharraf in December 2003. When the former United States President, George Bush took an administrative trip to London in November 2004, it was conveyed that the British police deliberated implementing jammers to safeguard the president's convoy through London.
Today, civilian application of jammers has been on the increase for private and government usage though limited to a specific range particularly for administrative use. The purchase and the usage of the mobile phone jammer have been at an all-time high, particularly in main large urban municipal regions. The real range of the jammer is contingent on its influence, power and the indigenous environment that might consist of hills or walls of a structure that could block the jamming signal. Low-powered jammers disrupt calls in a range of about 30 feet (9 m). High-powered units generate a mobile phone “dead” zone as enormous as a football field. Law Enforcement or military units can shut down service up to 1 mile (1.6 km) from the equipment (Pozar 2005).