|Kabir Muhammad Abdulmajeed (firstname.lastname@example.org)|
|Electrical and Electronic Engineering, Osun State University|
|A mobile phone jammer prevents communication with a mobile station or user equipment by transmitting an interference signal at the same frequency of communication between a mobile station and a base transceiver station. This project employs a system known as "active denial of service jamming" whereby a noisy interference signal is constantly radiated into space over a target frequency band and at a desired power level to cover a defined area. This jammer works dual-band and jams the downlink frequencies of the global mobile communication band - GSM 900 MHz and the digital cellular band - DCS 1800 MHz using noise extracted from the environment. It jams three well-known carriers in Nigeria (MTN, AIRTEL and ETISALAT). The operational block of the jamming system is divided into two sections: Intermediate frequency (IF) section and the Radio frequency transmitter module (RFT). The IF section comprises a Noise circuit which extracts noise from the environment by the use of a microphone, this noise is mixed with a tuning (ramp) signal which tunes the radio frequency transmitter to cover certain frequencies. The output of the IF is fed to the RFT which comprises an in-built voltage controlled oscillator, power amplifier and antenna connectors. An antenna radiates the jamming signal to space. Upon activation of the mobile jammer, all mobile phones will indicate "No-Network", "SOS" or "Searching-For-Service”, and all phones within the effective radius of the jammer are silenced. Incoming calls are blocked as if the mobile phone were off. When the Mobile jammer is turned off, all mobile phones will automatically re-establish communications and provide full service.
In conclusion, a jammer working on man-made (extrinsic) noise was constructed to interfere with mobile phones in places where mobile phone usage is disliked, offensive or forbidden.