In our day to day life, the usage of cell phones has increased enormously. So at present, silence and security are a major concern in examination halls, auditoriums, conference halls, meetings etc; so we attempt to implement the
?CELL PHONE JAMMER?.
??????????????????????????????????? Cell phone jammer is a device which allows to block or jam all the incoming and outgoing calls and SMS with in a specified area. It does not have any direct connection with the cell phone. It works on the same frequency band of which the cell phones operate.
???????????????????????????? Cell phone uses two technologies namely GSM and CDMA. The GSM uplink frequency ranges from 880MHz ? 915MHz and downlink frequency ranges from 925MHz ? 980MHz. CDMA uplink frequency ranges from 824MHz ? 849MHz and downlink frequency ranges from 869MHz ? 894MHz. The main objective of the proposed work is to block both GSM and CDMA frequencies.
INTRODUCTION:
1.1.An Overview to Cell Phone Jammer
??????????????????????????????????? A cell phone jammer is a device that emits signal in the same frequency range that cell phones use, effectively blocking their transmission by creating strong interferences. The power of the Jammer?s effect can vary widely based on a factors such as proximity to towers, indoor and outdoor settings, presence of building and landscape, even temperature and humidity play a role.
??????????????????????????????????? Jammer blocks cell phone use by sending radio waves along the same frequencies that cellular phones use. This causes enough interference with the communication of cell phones and the towers to render the phones unusage. Thus jammer can work by either disrupting phone to tower frequencies or tower to phone frequencies.
1.2.Global System for Mobile Communication
GSM is the most popular standard for mobile phones in the world. GSM is an open standard which is currently developed by the 3GPP. GSM networks operate at various frequencies most of them operate at 900MHz or 1800MHz.
??????????????????????????????????? There are four different cell sizes in a GSM network ? Macro, Micro, Pico and umbrella cells. The coverage area of each cell is different in different environments. Cell radius varies depending on antenna height, gain and propagation conditions from couple of 100Mtrs to several tens of kilometers. The longest the GSM specifications supports in practical use in 35 kilometers.
1.2.1. GSM Frequency Bands
??????????????????????????????????? There are five frequency bands used by GSM mobile phones.
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1.2.2. Subscribers Identity Module
?????????????????????????????????????? One of the key features of GSM is the Subscriber Identity Module (SIM), commonly know as SIM card. The SIM is a detachable smart card containing the user?s subscriptions information and phone book.
1.2.3. Advantages of GSM
1.3. Code Division Multiple Access
??????????????????????????????????????? CDMA, a proprietary standard designed by Qualcomm in the United States, has been the dominant network standard for North America and parts of Asia. CDMA has been traditionally faster than GSM. CDMA lets every one transmit at the same time. It works by assigning unique codes to all speech bits and the encrypted signal are dispersed over a wide frequencies spectrum of 1.25MHz. The signals are picked out by the receiver?s equipment that is tuned / programmed to identify that code. In contrast to GSM, same frequency channels are used in each cell.
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CDMA splits the sound in to small bits that travels on a spread spectrum of frequencies. CDMA technology allows a network to handle more calls than competing digital technologies.
1.3.1. Advantage of CDMA
BLOCK DIAGRAM
?2.1. INTRODUCTION
??????????? The Cell Phone Jammers works on the same frequency band of the cell phones operate ?Cell phone has a property of frequency shifting. When there is any disturbance on operating frequency will shift into the next channel. This continues operation keeps the cell phone link free from any interference and co-channel interference. The GSM band frequency is 925MHz-960MHz. The CDMA band frequency is 825MHz-860MHz.
??????????? In Cellular Communication system there are 124 channels available for any cell user. That means when any request is made the cell phone has to find which channel is free. In this process the cell has to search for free channels. During this process the cell phone takes 40 ?sec for searching between adjacent cells. The bandwidth between each channel is 200 kHz.
2.2. HYBRID OSCILLATOR? ?
???????? In order to block the cell phones, we have to generate Jamming frequencies with 40 ?sec scanning speed. The blocking range is 835 MHz to 980 MHz. But to the presence of variations in temperature, fluctuations in circuitry, we generate 800 MHz to 1000 MHz. Initially a spot frequency is generated in the range between 800 MHz to 1000 MHz. In order to spread the frequencies in the full range, scanning voltage is applied. The scanning voltage is varied and depending on the variations frequencies in the range 800 MHz to 1000 MHz is generated.
2.3. PULSE GENERATOR
??????????? The Pulse Generator is used to generate the pulses. These pulses are used to convert the analog signals into digital signals, since we use digital modulation in the cellular system. This can be done by
a pulse generator which produces pulses of 1 ?sec. The pulse generator uses TL084 CN QUAD op-amp consist of four op-amps.
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2.4. PINK NOISE GENERATOR
????????????? Another input to the modulator is ?Pink Noise?. The pink noise is generated by using pink noise generator. This noise is used as a message signal so that modulation stage results in producing noise in the cell phone frequency range and to create confusion in the hand set.
The noise generator is just a standard 6.8 volt Zener diode with a small reverse current and a transistor buffer. The (optional) National LM386-1 audio amplifier acts as a natural band-pass filter and small-signal amplifier. The noise jamming signal is then mixed with the triangle wave input. This will help in making the jamming transmission, making it look random ?noise? to and outside observer. Without the noise generator, the jamming signal is just a sweeping, unmodulated Continuous Wave (CW) RF carrier.
The LM386 based noise generator may break in to oscillation or Output very low signal. If does this, adjust the Zener bias resistor (2 k) up Down few hundred ohms while observing the signal (disconnected from the LM386) on an oscilloscope for the maximum noise signal. The grounding should be done properly. The LM386 will oscillate without a good grounding system and poor power supply bypassing.
???????????????? ?????????????????? Any Zener diode above or equal to 6.2 volts will work in the noise generator, as this Zener diode have an ?avalanche? region which generates a tremendous amount of noise when properly biased.
2.5. Modulator
??????????????????????????????????? The modulation of used is GSMK. GSMK means Gaussian Minimum shift keying, which is a continuous phase, frequency shifting keying process. That means only the phase is kept constant varying frequency of the carrier in accordance with the message signal which is pink noise here. For the modulation purpose an oscillator circuit with the variable capacitance diode is used here.
??????????????????????????????????? The frequency ranges used in the cell phone band are in MHz ranges so ordinary transistors are not enough for the modulation. So here high frequency transistors are used. The high frequency transistors used here is BFG 65. These transistors can be used for the MHz ranges.
2.5. Band pass Filter
??????????????????????????????????? Due to the modulation process some variations occurs which disturb other applications. So to avoid this and for gaining accuracy this complex signal waveform is passed through a 50 ?? a strip line filter. This special filter prevents GSM/CDMA pulsed signal from overshooting from specified band spectrum. Here the lower band and upper band are also limited by stripline filter.
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2.6. Preamplifier
??????????????????????????????????? The output power obtained is very low. This is not enough to drive the output MOSFET amplification section. In order to drive the MOSFET power module the preamplifier stage is used which produces an output of 2.5mV. The bandwidth corrected signal is connected to 2 dB attenuator before power module. The 2 dB attenuator is used to give correct impendence matching to the MOSFET power module. This is necessary because the output amplifier is build with MOSFET module which requires very low signal level to drive with effective impendence matching. The output module is mounted as far as from all other signal sources and power supply section to avoid stray RF noise coupling.
2.7. Output MOSFET Amplifier
??????????????????????????????????? The output module works from 3.6 V DC at 3 ? 5 current. This output module is more critical to assemble as even a low stray coupling may lead to strong oscillation and cause to overload the module, finally damage.
??????????????????????????????????? The power supply line is adequately decoupled with good quality low leackage capacitors and RF inductors. The heat produced by the module also should be radiated properly to keep the surface temperature within limit. Normally a good quality heavy duty heat sink with direct mounted module is critically coupled through strip line and inductive. The MOSFET power module used in the output stage has lot of advantages
This advantage makes the MOSFET power module as an ideal output device for this project.
2.9. WHIP 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.
??????????????? The output of the module is terminated to a whip antenna with correctly tuned matching network. This network helps to transfer the generated energy to the area without much loss. Correct impedance matching is necessary to keep the standing wave ratio as low as possible. Otherwise the return loss will hit up the output module causing permanent damage. A copper wire is used as whip antennas with 1/4th wave length. This antenna has a radiation pattern of 360?.
?????????????? The most important part of a radio system is the antenna. Directional gain antennas can be used to increase the jammer?s performance, but only in the direction the antenna is pointed. High-gain, omni-directional antennas are the best.
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