Designing A Rf Gsm Mobile Jammer Computer Science Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

This Final Year Project (FYP) title is RF GSM mobile jammer. The main purpose of this Final Year Project is designing a mobile jammer that enables user to jam the mobile devices at undesired places such as meeting room, class room, library, and worship places. The mobile device can jam all the mobile devices nearby. Therefore, it is required to design a complete system which contents power system, IF section and RF section. Basically, this device operates at GSM frequencies which are GSM900 and GSM1800. GSM 900 is a designed for extensive radio coverage even in rural areas. DCS 1800 is designed for radio coverage in areas with very high subscriber density. Communication jamming device was first developed by military .the device was used for denying the successful transport of information from the sender (tactical commanders) to the receiver (army personal),and vice-versa. Nowadays, the mobile devices are becoming very important for our daily life. Here in Malaysia, there are three telecommunication companies such as Celcom, Maxis and Digi. All of these telecommunication companies are using dual band of frequencies such as GSM900 and GSM 1800. Even thought using of cell phone is every important for our daily life but these cell phone devices are creating some problems as the sound of ringing becomes annoying or disrupting in our environment. So the device jammer is the solution to avoid the annoying or disrupting of the cell phone devices. As I mentioned early, the device jammer consists of three sections which are power supply, IF section and RF section. The technology behind the jammer device is that, RF section transmits signals in frequency range which is quite similar to frequency range of cell phone device. These signals which are coming out from jammer device will interface cell phone signals which results in a no network available display on cell phone screen.

1.3 Scope of Design

For this Final Year Project, there are quite a number of the Discrete Components Modules and Integrated Chip Modules. From the block diagram that is shown in Figure 1.1; the Discrete Component Modules cover the Voltage Controller Oscillator, Reference Oscillator. While the Integrated Chip Modules cover the Modulator, Mixer and Power Amplifier. Some designing software programs are used for this Final Year Project, such as Express PCB, PSpice and Multisim 8 are used for drawing the schematic diagram.

The lab equipments such as Vector Network Analyzer, Spectrum Analyzer, Oscilloscope and Signal Generator are used for testing the hardware modules. Further detail of the Discrete Component Modules will be discussed in Chapter 3 of this report. While for the Integrated Circuit Modules will be explained is detail in the chapter 4.

1.5 Project overview

The project consists of few chapters that will be handled. Naming and brief about these chapters are below:

Chapter 2: Literature review

In this chapter many previous researches in the iamming signals field and. In addition, their designs and building construction will be noted.

Chapter 3: Project's components Design details

This chapter will be about the components and their work regarding to the project fields and concepts which will be done. In addition it is like key points to chapter four that will contain the project main design part.

Chapter 4: Project circuit design and fabrication

This chapter will be about the whole project hardware designing and that will cover the circuits design, building and components chosen. Also it will cover things that need to be considered in constructing the device.

Chapter 5: Discussion on Project

Within this chapter the reports will be about the obstacles that faced while doing the whole project some are theoretical such as limitations and other are human been precision in designing the system. Lastly this chapter will cover and discusses the final output results achieved.

Chapter 6: Conclusion, future limitation and Recommendation

This chapter will be about the future limitation and some recommendation for the project. Finally conclusion will be given to provide a brief knowledge about the project.

1.6 Methodology

This project has been assigned to me as the final year project. The achievement of the whole project must be done with the specified period that is two semesters of the university studying plan. The project work would be divided into parts regarding to the time given. In the first trimester I started gathering information and searching for related researches that support the project. Also reading through the theoretical sources of the GSM jamming signal is done with the help and advice of the respective supervisor. At the same time many previous designed have been studied and comparison between them accrued. The end of the first phase I did a presentation about what have been done. The second phase is concerned about the final design that I have to come out with. Then I started gathering the components and all the sources of the hardware needed. After having all components building of the device has taking place at the time. Testing of the final design constructed and changes are made. Finally the output of the device has to be recorded for more than one time to figure out if there is any difference in the outputs achieved and then noting all the output within the final report which is called the documentation of the performance of the project.

Chapter 3: Project's components Design details

3.1 Chapter Overview

This Chapter covers the module that uses the discrete components or lumped components to build the circuit. The discrete component that is used for construct the circuiting the circuits are inductors, capacitors, transistors, resistors and diodes. The modules to be discussed in this chapter are Voltage Regulator, Reference Oscillator, Voltage Controlled Oscillator (VCO) and Antenna.

The implementation of jammer signal is quite hard ,the block diagram of the mobile jammer is shown in figure below:

Power supply

5,12,-12 volt

RF section

RF Jamming signals

IF section

Block diagram of mobile jammer

3.2 Voltage Regulator

3.2.1 Introduction

Every electronic and electrical device needs the power supply or voltage supply to power them up. For this project, all the circuit also required the voltage supply to power up. The voltage that is needed in this project is from 0.75V to 5V. A battery cannot exactly obtain the supply voltage that is required. Therefore a voltage regulator is used in this project. Besides, voltage divider is also used in this project to obtain the voltage values that cannot be obtained from the voltage regulator. For this section we will discuss the voltage regulator and the voltage divider that is used to obtain the different value of the voltage.

3.2.2 Specification and design procedures of Voltage Regulators

As discuss in the Chapter 1, RF transmitter consists of many modules. Different modules need different voltage to power up. The most common voltage used in this project is 12V and 5V. These two voltages values are converted from the Voltage Regulator and batteries as the source of voltage regulator.

The first voltage regulator used is the Voltage Regulator IC 7805. It is the voltage regulator that produces the output voltage 5V as long as the input supply is 6V to 12V. If the DC supply is more than 12V, the entire board will generate excessive heat and will damage the board.

Figure 3.1: Circuit and connection diagram of the 7805 Voltage Regulator

The connection of the 7805 Voltage Regulator required some lump component in order to obtain the stable voltage supply. The circuit board requires two pairs of 10uF and 0.1uF bypass capacitor to dampen the AC component or noise. The diode IN4002 is used to allow the current flow in one direction only. By building this circuit, a stable and low noise 5V voltage can be generated. Different circuit must be supplied the different voltage supply in order to power up the circuit. If the voltage supplied is over its limitation, the chip or component of the circuit will burn and cause the circuit board to damage. Hence when we want to connect the supply to the circuit board, we must be careful

3.3IF section

The IF section is an important part to generate desirable tuning signals for the VCO (voltage controller oscillator) in RF section. which will sweep the VCO through the desired range of frequencies. This tuning signal is generated by a triangular wave generator along with noise generator, and then offset by proper amount so as to sweep the VCO output from the minimum desired frequency to a maximum. IF section contains of four parts which are sweep generator, noise generator, summer and clamper.the circuit diagram of the IF section is shown below:

Circuit diagram of the IF section

3.3.1 Sweep generator

The main use of the triangle wave is to sweep the through the desired frequency range we want to cover the downlink through our VCO, i.e., 935-960 MHz for VCO66CL, and 1805-1880MHz for VCO55BE.

-555 timer IC: the operation of this IC revolves around the three resistors that form a voltage divider across the power supply, and the two comparators connected to this voltage divider. The IC is quiescent so long as the trigger input (pin 2) remains at +VCC and the threshold input (pin 6) is at ground. Assume the reset input (pin 4) is also at +VCC and therefore inactive, and that the control voltage input (pin 5) is unconnected. Under these conditions, the output (pin 3) is at ground and the discharge transistor (pin 7) is turned on, thus grounding whatever is connected to this pin.

The charging time for the capacitor can be found as follows:

For discharging time, the following equation can be used:

The output frequency can be calculated as follows:

In our project, we need to get the duty cycle (D.C.) equal to 50% which means the time needed for charging equals the discharging time. This can be done by using = and placing a diode across. The following equation shows the output frequency:

In our project, we used ==750 Ω with C=0.1 μF, then the output frequency is 10 KHz Since we use +12 V (Vcc), the output signal will be bounded from 4 V (Vcc/3) to 8 V (2Vcc/3). Figure 5 shows all the components used to generate the triangular wave. The output is shown in figure 6.

The schematic diagram of sweep generator

The output of the sweep generator

3.3.2 Noise generator

We have to generate noise signal in order to mix it with triangular signal to get tuning signals to supply VCO in RF section. The noise will help in masking the jamming transmission, observer. Without the noise generator, the jamming signal is just a sweeping, making it look like random "noise" to an outside unmodulated Continuous Wave RF carrier.the sechamatic diagram is shown below:

Schematic diagram of noise generator

In order to generate noise signal Zenar diode is used, which is operated in reverse mode. In the reverse mode avalanche effect is appeared which cause wide band noise. two amplification stages are used, which are:

- NPN transistor.

NPN transistor has three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. In our project we used npn transistor to amplify the noise signal.

NPN transistor

- LM386 IC.

The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value from 20 to 200.

The inputs are ground referenced and the output automatically biases to one-half the supply voltage. The quiescent power drain is only 24 milliwatts when operating from a 6 Volt supply, making the LM386 ideal for battery operation. To make the LM 386 a more versatile amplifier, 2 pins (pin 1 and 8) are provided for gain control. With pins 1 and 8 open the internal 1.35k resistor sets the gain at 20 (26 dB). If a capacitor is placed between pin 1-8, bypassing the built-in 1.35k resistor, the gain will go up to 200.

If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200. Gain control can also be done by capacitively coupling a resistor or FET transistor from pin 1 to the ground.

LM 386 Amplifier

3.3.3 Mixer or summer.

The operation of mixer is to add both of triangular and noise signals before entering VCO. In our project, LM741 IC was used. Triangular signal is connected to pin (2) and noise signal is connected to pin (3).12V is supplied to pin (7) and -12V is supplied to pin (4).

Block diagram of LM471

In order to amplify noise signal by 2, is used, so that the ratio of noise to sweep signal is 2:1.

The schematic diagram of mixer

3.3.4 Clamper

The circuits in Figure below are known as clampers or DC restorers. The corresponding netlist is in Figure below. These circuits clamp a peak of a waveform to a specific DC level compared with a capacitively coupled signal which swings about its average DC level (usually 0V). If the diode is removed from the clamper, it defaults to a simple coupling capacitor.

Clamper circuit

In order to get needed frequency range VCO must be bounded from 0 to 3.5V,so that the resistor R=100k is connected parallel with diode ,then R=100k was measured and found that:

Typical value

Measured value



When the 100-kΩ resistor was changed by 1-kΩ resistor, we note that some distortion appeared in the output signal; the reason is that for the circuit the time constant is


, so when R is not large enough, the voltage across the capacitor will discharge significantly during the interval the diode is OFF.