Jordan University of Science and Te

Jordan University of Science and Technology
Electrical Engineering Department
GSM-900 Mobile JAMMER
Done By:
Ahmad Jisrawi
Supervised By:
Dr. Nihad Dib

Table of Contents
Introduction ……………………………………………………………………… 2
Mobile Jamming and Disablers Techniques……………………………………… 3
GSM-Mobile JAMMING Requirements…………………………………………. 7
Design and Implementation of GSM Mobile JAMMER………………………….11
RF-Section ………………………………………………………………..11
Voltage controlled oscillator……………………………………....12
RF-Power Amplifier………………………………………………13
Antenna…………………………………………………………....15
IF-Section………………………………………………………………... 18
Triangular wave generator……………………………………….. 18
Noise Generator…………………………………………………... 20
Signal mixer and DC-offset Circuit………………………………..21
Power Supply………………………………………………………………24
Conclusions………………………………………………………………………...26
References………………………………………………………………………….27
1


INTRODUCTION
A 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 are disabled.
Communication jamming devices were first developed and used by militar y. Where
tactical commanders use RF communications to exercise control of their forces, an enemy
has interest in those communications. This interest comes from the fundamental area of
denying the successful transport of the information from the sender to the receiver.
Nowadays the mobile jammer devices are becoming civilian products rather than
electronic warfare devices, since with the increasing number of the mobile phone users
the need to disable mobile phones in specific places where the ringing of cell phone
would 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 o f their mobile phone
become very annoying specially during the praying time.
Figure 1: Typical sign used in places where
mobile phone are not allowed
2

Mobile Jamming and Disablers Techniques
There are different approaches to prevent mobile phones from ringing in specific area,
the main five appro aches 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 ov erpower 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 o f R F interference)
prevent all pagers and mobile phones located in that area from receiving and
transmitting calls. This type of device transmits only a jammin g sign al 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, “Ther e are two types. One is called b rute 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 cap able to communicate with the cellular base station. When the
3

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 estab lishment 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. In
the coverage area of the beacon only terminals which have a compatible receiver
would respond and this should be built on a separate technology from cellular/PCS,
for example Bluetooth technology. Also the handset must re-enable its normal
function as it leaves the coverage area of the beacon.
The need for intelligent handsets with a separate receiver for the beacon receiver
from the cellular/PCS receiver, make eff ective deployment for the type "C" device
will be problematic for many years.
4

4-
Type "D" Device
This jammer is similar to type "A" , but with a receiver, so that jammer is
predominantly in r eceive mode and when the device detects the presence of a
mobile phone in the "silent" room; it will intelligently choose to interact and block
the cell phone b y transmitting jamming signal. This jam signal would only stay on
as long as the mobile continues to make a link with the base station; otherwise there
would be no jamming transmission.
Thus this device much less electromagnetic pollution in terms of raw po wer
transmitted and frequency spectrum from the type "A" Jammer, and ther efore much
less disruptive to passing traffic. This technique could be implemented without
cooperation from PCS/cellular providers. Also this technique has an added
advantage over Typ e B in that no added overhead time or effort is spent negotiating
with the cellular netwo rk.
5-
Type "E" Device
This technique is using EMI suppression techniques to make a room into what is
called a Faraday cage. Although labour intensive to construct, the Faraday cage
essentially blocks, or greatly attenu ates, virtually all electromagnetic radiation from
entering or leaving the cage or in this case a target room.
With current advances in EMI shielding techniques and commercially available
products one could con ceivably implement this into the architecture of newly
designed buildings for so-called “quiet-conference” rooms.
Emergency calls would be blocked unless there was a way to receive and decode
the Emergency Call transmissions, pass b y coax outside the room and re-
transmitted.
5

This passive configuration is currently legal in most worlds' countries for any
commercial or residential location; however some building may not allow this type
of construction. Table 1 shows a comparison between the different
Jammer/Disablers techniques.
Emer gency
Regularity
Type
Efficiency
Implementation
call
Approval
Not
"A" Blocked Low
Ver y simple
allowed
Complex
"B" Allowed Medium Required
(Required third party
Cellular/PCS Services)
Complex
"C" Allowed High Required
(Required Intelligent Handset)
"D" Allowed Medium Required Simple
High(No sign al
"E" Blocked
Allowed Simple
transmitted)
Table 1: Comparison between Jammer/Disabler Techniques
6

GSM-Mobile JAMMING Requirements
As discussed in part-2, jamming objective is to inject an interference signal into
the communications freq uency so that the actual signal is completely submerged by
the interference. It is important to notice that transmission can never be totally
jammed - jamming hinders the reception at the other end. The problem here for the
jammer is that only transmitters can be found using direction finding and the
location of the target must be a specific location, usually where the jammer is
located and this is because the jamming power is never infinite.
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 b e compensated b y error correction.
Usually a successful jamming attack requires that the jammer power is roughly
equal to signal power at the receiver.
The effects of jammin g depend on the jamming-to-signal r atio (J/S), modulation
scheme, ch annel coding and interleaving of the target system.
Gener ally Jamming-to-Signal r atio can be measured according to the following
Equation. [2]
J
G
G
P
R
L
B
2
=
j
j r
r j
t r
r