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GSM-900 Mobile JAMMER
INTRODUCTION
A GSM Jammer is a device that transmit signal on the same frequency at witch theGSM system operates, the jamming success when the mobile phones in the area wherethe jammer is located are disabled.
Communication jamming devices were first developed and used by military. Wheretactical commanders use RF communications to exercise control of their forces, an enemyhas interest in those communications. This interest comes from the fundamental area ofdenying the successful transport of the information from the sender to the receiver.
owadays the mobile jammer devices are becoming civilian products rather thanelectronic warfare devices, since with the increasing number of the mobile phone usersthe need to disable mobile phones in specific places where the ringing of cell phonewould be disruptive has increased. These places include worship places, university lecture rooms, libraries, concert halls, meeting rooms, and other places where silence is appreciated.Mosques are example for the places were mobile jammer would be a great solution, although mosques asks politely from prayers to disable their mobile phone during the prayer ,see figure (1), some people forget and the ringing phone of their mobile phone become very annoying specially during the praying time.
Mobile Jamming and Disablers Techniques
There are different approaches to prevent mobile phones from ringing in specific area, the main five approaches used or being developed are described in RABC Mobile & Personal Communications Committee’s (M&PCC) meeting of June 22, 1999 [1], these techniques are summarized in this section :
1- Type "A" Device
In this device we overpower cell phone's signal with a stronger signal, This type of device comes equipped with several independent oscillators transmitting ‘jamming signals’ capable of blocking frequencies used by paging devices as well as those used by cellular/PCS systems’ control channels for call establishment.
When active in a designated area, such devices will (by means of RF interference) prevent all pagers and mobile phones located in that area from receiving and transmitting calls. This type of device transmits only a jamming signal and has very poor frequency selectivity, which leads to interference with a larger amount of communication spectrum than it was originally intended to target.
Technologist Jim Mahan said, “There are two types. One is called brute force jamming, which just blocks everything. The problem is, it’s like power-washing the airwaves and it bleeds over into the public broadcast area. The other puts out a small amount of interference, and you could potentially confine it within a single cell block. You could use lots of little pockets of small jamming to keep a facility under control.”
2- Type "B" Device
This device also called "Intelligent Cellular Disablers devices", and it does not transmit an interfering signal on the control channels. The device basically works as a detector, and it capable to communicate with the cellular base station. When the device detects the presence of a mobile phone in the "silent" room; a prevention of authorization of call establishment is done by the software at the base station. The
device signals the base station that the target user is in a ‘quiet’ room; therefore, do not establish the communication. Messages can be routed to the user’s voice- mail box, if the user subscribes to a voice- mail service. This process of detection and interruption of call establishment is done during the interval normally reserved for signaling and handshaking.
This intelligent device as it’s name imply can recognize emergency calls and also can allow specific pre-registered users to use their mobile phones for a specified duration. Although this device sounds the best solution for disabling mobile phone, a provision is needed by the cellular/PCS service providers or provision by a third- party working cooperatively with full support of the cellular/PCS service providers, allowing the detector device to be integral part of the cellular/PCS systems.
3- Type "C" Device
This device also called "Intelligent Beacon Disablers ", as in the type "B" device it does not transmit an interfering signal on the control channels.
The device, when located in a specific "silent" room, functions as a ‘beacon’ and any compatible terminal is ordered to disable its ringer or disable its operation. Inthe coverage area of the beacon only terminals which have a compatible receiverwould respond and this should be built on a separate technology from cellular/PCS,or example Bluetooth technolo. Also the handset must re-enable its normalfunction as it leaves the coverage area of the beacon.The need for intelligent handsets with a separate receiver for the beacon receiverfrom the cellular/PCS receiver, make effective deployment for the type "C" devicewill be problematic for many years.

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GSM-900 Mobile JAMMER
INTRODUCTION
 JAMMING is the act of intentionally directing electromagnetic energy at a communication system to disrupt or prevent signal transmission.
 The GSM Jammer is a device that transmit signal on the same frequency at witch the GSM system operates, the jamming success when the mobile phones in the area where the jammer is located could’nt make or reciece call phones .
JAMMING Techniques 1
 Type “A”: JAMMERS
 Type ”B”: Intelligent Cellular Disablers
 Type “C”: Intelligent Beacon Disablers
 Type ”D”: Smart JAMMERS
 Type ”E”: Faraday Cage ( EMI Suppression Techniques)
GSM JAMMING Requirement 1
 Jamming is successful when the jamming signal denies the usability of the communications transmission. In digital communications, the usability is denied when the error rate of the transmission cannot be compensated by error correction.
 Usually a successful jamming attack requires that the jammer power is roughly equal to signal power at the receiver.
 The effects of jamming depend on the jamming-to-signal ratio (J/S), and the modulation scheme.
GSM JAMMING Requirement 2
Jamming-to-Signal ratio is given by:
Where:
Pj = jammer power
Pt = transmitter power
Gjr = antenna gain (jammer to receiver)
Grj = antenna gain (receiver to Jammer)
Gtr = antenna gain (transmitter to receiver)
Grt = antenna gain (receiver to transmitter)
Br = communications receiver bandwidth
Bj = jamming transmitter bandwidth
Rtr = range between communications transmitter and receiver
Rjt = range between jammer and communications receiver
Lj = jammer signal loss (including polarization mismatch)
Lr = communication signal loss
GSM JAMMING Requirement 3
 The frequency of the transmitted signal of the jammer must cover the GSM frequency range
 As the power received from the GSM Base Station is usually low, It is easier to jamm the downlink (i.e. Jamming the mobile station 'handset' receiver) than uplink, hence the jammer output frequency should cover the downlink frequency.
Design and Implementation
GSM Mobile JAMMER
GSM-900 Mobile Jammer
RF-Section 1
 The RF-section is responsible for generating and transmitting the RF-Jamming signal. The main parts are: VCO, Power Amplifier, and the Antenna.
 fortunately, all the parts used are internally matched to 50ohm load, and hence transmission lines used are microstrip lines designed to have 50ohm characteristic impedance
 The components used are all surface mount component
GSM-900 Mobile Jammer
RF-Section 2
 The output power of the jammer was designed so that it has a range of 20m, and was calculated as follow:
 Jr ( jammer power at mobile receiver) ≥ Smax – SNRmin
SNRmin = 9 dB for mobile receiver and
Smax = -15dBm (Mobile station signal power at mobile receiver)
Jr ≥ -24 dBm
 The jammer output power = Jr + F
free space path loss equation:
F = 32.45 + 20 log (f *D), f in MHZ and D in Km
Output power = 58 – 24 = 34 dBm
GSM-900 Mobile Jammer
RF-Section 3
The VCO 1
 The MAX2623 VCO from MAXIM IC was used to generate the required signal
 The output frequency range for the VCO is:
850 – 1000 MHz for a tune voltage from 0.4 – 2.6V.
 The input tune frequency best suited the VCO was 120KHz to sweep the desired frequency range.
GSM-900 Mobile Jammer
RF-Section 4
The VCO 2
 The MAX2623 VCO is implemented as an LC oscillator configuration, integrating all of the tank circuitry on-chip.
 The tuning input which control the output frequency is internally connected to the varactor.
 The output is internally matched to 50ohm, and output power of -3dBm.
GSM-900 Mobile Jammer
RF-Section 5
The VCO 3
GSM-900 Mobile Jammer
RF-Section 6
RF Power Amplifiers 1
 Two RF power amplifiers were used to achieve the required output power (i.e. 34dBm).
 The first stage power amplifier was the MAR-4SM from Mini-Circuits it has a gain of 8dB for frequency range from DC to 1000 MHz
so the output of this stage should be 5dBm
for the -3dBm output of the VCO
GSM-900 Mobile Jammer
RF-Section 7
RF Power Amplifiers 2
 Input and output are matched to 50hom load
 The MAR-4SM is current biased power amplifier
GSM-900 Mobile Jammer
RF-Section 8
RF Power Amplifiers 3
 The second stage power amplifier is the Hitachi PF08103b dual power amplifier with efficiency at 48%.
 It can operate either on GSM-900 or DCS1800, so external circuitry was designed to configure it to operate in GSM mode
 The output of the power amplifier is 35dBm
for 1dBm input
GSM-900 Mobile Jammer
RF-Section 9
RF Power Amplifiers 4
 Symmetric T-Network with 4dB attenuation was used To obtain 1dBm at the input of the second power amplifier from the 5dBm output of the first power amplifier.
 For 4-dB attenuation, and matched to 50ohm transmission line, V-2 = V2 = 0.631 * V1
(S12 = S21 = 0.631) the value of the resistors was found using the following equations
0.631 = (X / (X + R1))*(50 / (50 + R1)
50 = (R2 + 50) // (R3) + R1
where X = (R2 + 50)//R3.
GSM-900 Mobile Jammer
RF-Section 10
The Antenna
 1/4 wave monopole antenna, with center frequency at 916Mhz and bandwidth of 150 MHz.
 50 ohm impedance
 VSWR < 1.7
 Gain 2dBi
 Connected to the RF-Section using RP-SMA connector
GSM-900 Mobile Jammer
RF-Section 11
 GSM-900 Mobile Jammer
RF-Section 12
 GSM-900 Mobile Jammer
IF-Section 1
 The function of the IF-section of the Mobile jammer is to generate the tuning signal required by the VCO in the RF-Section
The main parts of the IF-Section are:
 Triangular Wave Generator
 Noise Generator
 Signal Mixer and DC offset
GSM-900 Mobile Jammer
IF-Section 2
Triangular Wave Generator
 The circuit used to generate the triangular wave is the 555-Timer as ASTABLE MULTIVIBRATOR
 The output frequency is given by the following equation:
 Fr = 120 KHz
 GSM-900 Mobile Jammer
IF-Section 3
Noise Generator 1
 Noise will help in masking the jamming transmission, making it look like random "noise" to an outside observer.
 The noise generator used is based on the avalanche noise generated by a Zener breakdown phenomenon.
 The noise generator circuit consists of:
 A standard 6.8 volt Zener diode with a small reverse current
 Transistor buffer
 National LM386 audio amplifier function as:
 Small signal amplifier
 Band pass filter
GSM-900 Mobile Jammer
IF-Section 4
Noise Generator 2
 GSM-900 Mobile Jammer
IF-Section 5
Signal Mixer and DC-Offset Circuits
 The triangle wave and noise signals are mixed using Op-Amp configured as summer.
 A DC voltage is added to the resulted signal to obtain the required tuning voltage using Diode-Clamper circuit.

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