Cell Phone and Wireless Access Jammers

Cell Phone and Wireless Access Jammers

Nowadays, Mobile phones of cell communication and electronic devices  which intercept the information (a covert listening device), based on their principle are increasingly used for the interception of voice information Besides, specially designed and modified smart phones, or even  models, bought in electronic store (cell  phones) can be used for  wiretapping of conversations in rooms.


The simplest and the most common way of using  a cell phone as a covert listening  device (in short for “bug”) is the inclusion of transmission by dialing a telephone number from which intercepted conversations will be recorded  and hidden installation of this mobile device in a controlled environment.

A cell phone can be used as a means of interception when using the active complex of interception of cellular communications, which is a virtual reference station (VRS)  within the GSM network, applying for intercepted from a real network parameters of a cell, which is authenticated with cell phones  as a normal base station.



When you turn on the  virtual base station at a relatively small distance from the monitored mobile device , the last one is  registered with it in accordance with the GSM standard. From this moment it is possible to manage  the mobile device  with the help of VRS, until the phone is  in transmit mode without any indication and without the consent of the owner (the so- called  “police regime”). When  installing a  special software on a mobile phone  you can activate “police mode”  without VRS.

There are many companies producing mobile phones with modified spy functions. For example, the English firm GSMS.ru is specialized on the modification of Siemens cell phones and the Italian Endoacustica is  on the modification of Nokia cell phones.

The first and  the cheapest type of modified phone is called the “switched off”. Special program changes the operation mode of the mobile phone when receiving incoming calls. If you install the simple version of this program,  when receiving an incoming call a  mobile phone goes to the auto answer without visible signs of the incoming call (phone doesn’t “emit”  light, sound or vibration signals).

When you install more complicated software, a mobile phone goes to auto answer without visible signs of an incoming call only when receiving an incoming call from a certain “control phone”, the incoming calls from all other phones is carried out in the usual manner

A more expensive type  of modified phone is  a “spy” phone (spy phone). In this device there are “tied” two numbers. Incoming and outgoing calls with the first (known) numbers are as in a normal phone. Incoming calls on the second (secret) number are made secretly, without visible signs of an incoming call.

Unlike cell phones, a  covert listening device (bug), is built based on them, but  have a much smaller size and can be installed in the interior of the controlled room secretly. In addition,  these devices can  be integrated into the network extenders, table electric lamps, electrical and radio equipment and their power supplies. Such devices are often called GSM bookmarks. The inclusion of standard GSM-bookmarks is usually carried out  with the transfer of the SMS message, or the  call to a phone number written in its SIM card. When receiving an SMS message,  the device will dial a phone number that is recorded in the SIM card memory beforehand  or mentioned  in the SMS.

After the connection  the  intercepting is accomplished  within a radius of 5-7 m from the installation site of the device and their transmission to the receiving point via a cellular communication channel.

When you receive a call, the mobile phone system  determines  caller’s phone number.  In case of  the  coincidence of this number with the number (one of numbers) stored in the SIM card memory,  there is a communication establishment  and  then  transmitting the intercepted information to the phone number of the caller. The interception is terminated (the bug is off) when the phone is unplugged of the receiving point.

Switching on and off of the  covert listening device is not accompanied by any sound effects, so its actual location can only be detected by the presence of radio emission. More complex covert listening devices are equipped with built-in digital recorders. The inclusion of a tape recording  is made by sending  an appropriate SMS-message with indication of the beginning and the end of the recording. Recorded on a digital recorder conversations can be overheard, or transferred to the receiving item to the data transfer mode.


The most effective and  the cheapest way is  to protect allocated areas from the interception of voice information  with technical means.  They  are called suppressors or cell phone signal jammers /blockers. They are  based on the cell phones and called cell phone signal jammers or cell phone signal blockers. These devices can be divided into three groups.

The first group includes cell phone blockers which  represent the generators of interference with manual control that provides the setting defensive interference noise in the frequency range of operation of base relevant standard stations.

The setting  of such interference leads to the  failure of the mobile phone management in base station of cellular communications and therefore the impossibility  to transfer the information. At the same time on the phone  screen the icon signal disappears, but appears  the message “Searching for network”.

The most widely  used in these  jammers  are  generators with  sawtooth restructuring of the carrier frequency. The noise generator includes: a high-frequency generator on the basis of the voltage controlled generator, the generator of sawtooth voltage, bandpass filter, power amplifier, a matching device and the antenna. The radiation frequency of the high frequency generator varies with the voltage within a given bandwidth ΔF = F2 – F1 (the frequency range of the standard cellular connection).

The control voltage is a sequence of sawtooth pulses. The signal output from the generator is supplied to a bandpass filter with a bandwidth of ΔF, where the suppression of out-of-band radiation is amplified and through a matching device is fed into the antenna. Thus, the generator emits a noise barrage interference in a given frequency band ΔF. To ensure the required efficiency of the cell phone jammer, the changing speed of the sawtooth control needs to be quite high.

For example, a  for  a cell phone jammer “Alligator”, the repetition frequency of the sawtooth pulse should be  about 275 kHz. With the aim of increasing the effectiveness of blocking signal  some cell phone jammers  use noise modulation of high-frequency signal.

The control voltage supplied to the generator, is an additive mixture of sequence of  sawtooth pulses and “white” noise, so it changes not only the frequency of the radiation, but also  the low frequency of  modulated noise signal.

The most simple mobile phone blockers instead of sources of low frequency noise signal can use low-frequency generators of sinusoidal voltage and there is no available bandpass filters in these models. However,  such jammers are characterized by high levels of out-of-band radiation and their effectiveness is much lower in comparison with mentioned model of  cell phone jammers.

The number of generators of interference included in the cell phone jammers  is determined by its purpose and is usually from 2 to 4.

As for the  antennas in cell phone blockers a telescopic whip antenna and the internal pin and loop antennas are used. The number of antennas, as a rule, corresponds to the number of suppressed communication standards.

The cell phone  blockers are mostly used by generators of interference with the radiation power in each channel from 0.5 to 2 watts. However, there are blockers with the radiation power of 8-10 watts or more. Such phone blockers are used to protect larger areas such as conference rooms.

One of the main characteristics of cell phone signal jammers is the radius of blocking zone, which depends not only from the capacity of the generator noise, but also from the removal of the base station: the further base station from the place of installation of the jammer, the greater the blocking range.

Considering that the blockers are mainly intended for installation in selected areas, they can operate  from the mains 220 V/50 Hz. Some cell phone blockers have an independent power source (batteries). Such blockers are mainly used for the protection of confidential negotiations in the car or unequipped confidential negotiations areas. Distortion of these jammers is from 70 mW to 0.25-0.5 W, which ensures blocking of moble phones within a radius of 2-5 m. When it’s used as a power source of two AA batteries with a capacity of 2700 mA/h the continuous operation time of the jammer can be from 30 to 60 minutes.


The use of cell phone jammers can be camouflaged as the various objects, such as a desktop clock, a radio, a cell phone or a pack of cigarettes to guarantee the secret policy.

The most widely used  are cell phone signal jammers of standard GSM. They include two jamming device operating in the frequency range 925-935 from to 960 MHz and from 1805 to 1880 MHz.

Nowadays in Russia the CDMA standard is gaining its popularity.  Most modern jammers include three blocking generators, two of them  – to block the cell phones of standard GSM, and one  is to suppress the cell phones of standard CDMA 2000 (frequency range of 462-468 MHz generator).

To block cellular communication of new generation 3GIMT-2000/UMTS (frequency range from 2010 to 2025 and 2125-2170 MHz) special models of jammers are used.


Some jammers use blocking generators  with extended ranges, which allows to fullfill a cell blocking not only GSM format.  For example, using a cell phone jammer operating in the frequency range from 860 to 960 MHz, it is possible to suppress mobile phones, not only GSM 900, but cell phones  standards AMPS/DAMPS, CDMA 800, etc. The extension of the range of the jammer from 1880 to 1900-1950 MHz allows to  block  communication and wireless access DECT.

The main advantage of the first type of blockers is a simple structure, but the disadvantage is that  the blocking begins immediately after the generator switches on. However, they block cell phones no matter if they are in required room or not.

The second group includes cell phone jammers with the control unit turning on the blocking generator.

The structure of the control unit includes a multichannel . The elements  of a multichannel receiver includes: a wideband antenna, bandpass filters, high frequency amplifiers, diode detectors, direct current amplifiers and a threshold device with adjustable threshold level.

The principle of the receiver operation is similar to the principle of  indicator operation of the electromagnetic field. When  you establish a connection, it means that you answer the call or transmit the call signal, the transmitter of the mobile phone of cellular connection is activated by radiation. High-frequency radio signal caused by this radiation and induced in the receiver antenna, using a splitter and bandpass filter (the frequency range of the respective standards of mobile communication) is supplied to the amplifier and then to a diode detector and a DC amplifier. Amplifier output signal is sent  to a threshold device. In case of exceeding the threshold, the signal is sent to the management device that issues a command (signal) in the power supply to switch on the noise generator of the corresponding frequency range. The jammer turns on for a few seconds. In the formulation of a broadband barrage interference is the failure of communication.

The receiver can be built into the  jammer’s body, or designed as a separate unit (module). The presence of multi-channel receiver allows the use of a blocking system in two modes.

The first mode (detection) is used to detect (identify) transferring cellular communication devices. It is intended for a covert identification of  electronic devices which intercept information based on the cell phone phones in a required room. Moreover, it’s used  to activate “police mode” in cell phones during confidential negotiations.

In the second mode (detection -blocking) is the automatic detection and blocking of all transferring  devices of cellular communication. This mode is typically used during confidential negotiations and meetings. The radius of the zone of suppression is governed by the power levels of the jammers.


The typical blocking system  of this class may include a detection  and blocking of the cell phone Hammer. The system consists of two modules: a special receiver detecting cell phones and jammer C-GUARD 100. These modules can work both together and separately.

A special receiver is  designed to detect mobile phone radiation  in the frequency range 820-920 MHz (communication standards GSM 900, AMPS, TDMA and CDMA IS-95) and 1700-1880 MHz (the communication standards DCS-1800, CDMA 2000). The receiver sensitivity is – 47 dBm (2×10-8 W) in the frequency range 900 MHz -45 W (3,2×10-8 W) – in frequency range 1800 Mhz, which is sufficient to detect the working cell phone within any office. Upon detection of radiation cell phone receiver runs a prerecorded voice message with a duration of 3 to 7, after which a cell phone jammer turns on automatically.

As a jammer in the Hammer system a cell phone blocker C-GUARD 100 is used. It provides blocking of cellular phone communication standards GSM-900 and DCS-1800 in the radius of 2 to 10 m. Intellectual cell phone blockers belong to the third group of jammers. It is different from the second group by the presence the block of digital processing of signals in their receptor

The phone jammer RS Jammini is intended for blocking of cellular communication of standard GSM. It  includes a panoramic receiver, the digital processing unit signals, a generator of pulsed narrowband interference and barrage jamming generator.

The Jammer receiver detects the mobile phone in the monitored area which is incoming in the communication or working in the mode of the transmission of information for a short period of time (about 300 µs). It  calculates the number of the frequency channel and time slot assigned to the phone.

After the establishment of frequency-time parameters of the detected mobile phone the  jammer is configured to the  frequency channel control of  this phone base station. Blocking  is performed with the help of short pulses with a duration of 300 microseconds, following with the period 4,616 ms each at the time of transmission of control signals by the base station. Total time of radiation of blocking signal when the mobile phone is establishing connection does not exceed 0,05-0,07 sec.  The width of the signal spectrum does not exceed several tens of  khz.

When the receiver  detects mobile phone  operation mode, with frequency jumps (“frequency hopping”) a blocker goes into setting defensive interference in the entire frequency range of operation of the base stations of the communication standard. The radius of the blocking zone  is significantly reduced. Consequently, the blocking process is  provided by the inability of the outgoing and incoming calls  and  SMS  messages .

The level of the emitted blocking does not exceed 0.7-1.0 W and commensurate with the level of radiation mobile cell phone, which meets the requirements of the international GSM standard for subscriber equipment and the applicable sanitary and hygienic norms.  As an antenna in the jammer there is  a dual band external antenna.

The power of the blocker is made from AC 220 V through a special adapter. The  jammer is designed for installation in areas where the number of simultaneously operating on mobile phones does not exceed two to three pieces, which significantly limits its application.

The mobile version of the  jammer is  equipped with integrated battery (3XAA) and has a shortened antenna. Phone blockers RS Jammini SL and RS Jammini UMTS” refer to smart cellular standards CDMA, WCDMA/UMTS. The principle of operation of these jammers is as following .

The blocking receiver detects the radiation of  mobile phones CDMA or UMTS  for a short interval of time (about 8 MS) and the control unit issues a command to the formation of  the blocking signal that is emitted in all “frequency trunks” of base station transmitters within 5 s, which leads to the disruption of the communication session. After this time the jammer returns to the detection mode.

The Power of the  blocking signal at the output of the amplifier is 0.3-0.4 W, which provides a range of suppression of the order of 5-10 m. The average time of blocking in the mode of establishing the connection is 2-5, but in the mode of transmission of voice information 10-15 C.

Cell phone jammers are designed for installation in classrooms and meeting rooms where the number of  phones does not exceed 4-5 pieces.

As a rule , intellectual cell phone jammers  are designed to block the phones of cellular communication of the standard, however, there are such kind of jammers  that provide the suppression of  mobile phones of  multiple standards. For instance, such devices  as RS “Multijam-mer (RS/MJ) and  “Chameleon-450/900/1800/2100” are  able to block mobile phones locally and to monitor  the required space

1. Complex RS/MJ is designed to block  the cellular and wireless access to any existing standards within a given zone.

2. RS/MJ can be operated around the clock, has a self-diagnosis and provides:

  1. the control of cellular communication ranges and wireless access of panoramic receivers;
  2. directed blocking of the base signal and the access point addressed to the caller attempting to establish a connection.

Blocking signal  has a minimum power and a pulsed structure, which effect is  much weaker  affected on humans than directly from a cell phone.

Complex RS/MJ performs the following tasks:

  • in the monitoring mode it produces detection enabled caller’s terminal or a cell phone at the time of the airing of his transmitter and evaluates its parameters (standard, channel number (carrier frequency), signal);
  • in the reduction mode it reduces the base station signal and blocks detected duplex channel at the time of transfer of the given (revealed) information to the abonent;
  • in offline mode (without operator and control computer) it blocks the working and included in the communication abonent’s terminal,  user remains in the  the network service, but the signal call  doesn’t pass.

Complex RS Multijammer” allows you:

  • to carry out the gain control of the receiving tract and the threshold detection for each of the standards separately, which allows you to adjust the blocking zone under the conditions of the required room, with the possibility of saving the data settings;
  • to turn on and off the blocking mode for each of the standards;
  • in the operator’s service mode the operator can display the computer information on abonent’s broadcast;
  • in all modes to keep abonent’s records in the controlled area.

The system provides remote control and operation in a computer network. The architecture of the complex allows to assemble equipment in accordance with solving tasks.

The basic elements of the complex are:

  • a singleboard panoramic receiver RS mini -receiver built as a direct down converter and an integrated system DSP;
  • the blocking signal driver containing eight two-band synthesizers with the control and communication controllers;
  • the set of basic power amplifiers;
  • the set of antennas.

The proposed approach allows to design the system either as integrated or as distributed in space. The concept allows us to produce the equipment in any configuration, for example GSM, PCS, EGSM, UMTS, CDMA-2000, wifi, WiMAX, DECT.

Complex local  cell phone blocking “Chameleon-450/900/1800/2100” is designed to  block cellular communication standards EGSM-900, DCS-1800,CDMA-2000hUMTS(3G). The complex includes a transceiving module, three external transmitting-receiving antennas , a personal computer and special software, Here you Нате-leon.

The principle of operation of this complex differs from the principle of operation of the RS/MJ significantly and is as follows .

The complex  receiver doesn’t only  monitor frequency range  of transmitters’ operation  of cell phone phones, but also it  carries out the reception and digital processing of signals in the whole range of transmitting frequencies of base stations of the corresponding standard.                                                                                         

According the results of this processing the list of frequency channels of base stations operating in protected zone generates, with an indication of the levels of the received signals.

The control unit of the generator noise on each of the detected frequencies (frequency channels) generates the blocking signal.

The power of blocking signal is installed depending on a power of a received signal from the base station, and the signal is formed by converting the received signal of the base station according to a certain algorithm and represents the kind of relay simulation hindrance.

When you activate the blocking mode the signal is radiated simultaneously in all detected frequencies of operating base stations, which leads to the disruption of the communication session in any modes of cell phone  system, including in the mode of frequency hopping. The maximum integral  blocking signal power is 0.7 watts on all channels .


The practice of application of this  complex showed that the  blocking of cellular communication in the area protected by the required power of blocking signal in each channel should be 10-100 mw, which is 15-20 dB less than a power of cell phone jammers  with barrage  blocking frequency.

The system can operate in one of two modes: “detection – blocking” or “blocking”.

In the first case the blocking is performed automatically upon detection by the receiver of a complex mobile phone radiation. The duration of emission of blocking signal is several tens of microseconds, after which the complex returns to the detection mode (search) mobile phone signals. After the disconnection (termination of mobile phone radiation), the blocking  stops.

The time of   the blocking mode in case of establishing  the incoming or outgoing communication of mobile phone is about 2-3 s. During a mobile phone blocking  with an established connection and located in the voice channel, the blocking interval increases, however, as a rule, does not exceed 20 sec. In the first mode  the blocking area of the complex is governed not only by the the blocking power  signal, but the sensitivity of its receiver.

The second mode is used when the mobile phone radiation level  is insufficient for reliable detection by the receiver of this complex. In this mode, it’s possible to activate the jamming device only  in manual mode. Blocking zone in this mode is determined only by the power of the blocking signal.

Based on the second and third types of cell phone jammers  the distributed system  is designed to suppress cellular communication in several large rooms, halls, floors, and separate buildings or in closed areas.  Besides, in each required the necessary blockers are installed, which are combined in a local network . For laying the network, you can use any bus type: twisted pair, optical fiber, radio channel, etc.



Each individual  phone blockers solve the cell phone blocking  problem in a given location. The blocker’s setting should be fulfilled in accordance with its individual peculiarities of location.

Information about mobile phone’s broadcasting in controlled areas with  time indicators  to the control computer on a local network.

With the host computer, the switch on/off blocking mode can be activated remotely to regulate the blocking  area and to diagnose the health of the system.

Except the secret listening devices blocked by  cell  phone jammers for transmitting  information it’s widely used such  wireless means as  Wi-Fi, Bluetooth, Wi-Max etc.

For their blocking special kinds of jammers can be used. Their operating  principles do not differ from cell phone jammer’s  principles.

For comprehensive protection of the allocated area multi-standard jammers can be used, including both cell phone jammers and jammers of the wireless access.

The installation in the selected areas such kinds of wireless and cell phone jammers will eliminate the possibility of intercepting ongoing confidential conversations with the help cell phones or other covert listening devices, constructed on the basis of the cellular and wireless access.

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