CURRENT STATE AND TACTICAL CAPABILITIES OF USING ELECTROMAGNETIC RADIATION INDICATORS..
LOBASHEV Aleksey Konstantinovich, Candidate of Technical Sciences, Associate Professor,
LOSEV Lev Sergeevich
CURRENT STATE AND TACTICAL POSSIBILITIES OF USING ELECTROMAGNETIC RADIATION INDICATORS
Devices designed to detect equipment for unauthorized transmission of information outside the controlled area occupy an important place in the arsenal of information security tools. Electromagnetic radiation indicators are among the products of this group. Among the search equipment they occupy one of the leading places and are an integral tool in conducting search activities. An attractive feature of these products is their simplicity, low price, and the ability to detect almost all types of radio signals, including such “complex” ones as broadband noise-like signals, signals with pseudo-random hopping of the carrier frequencyetc. As the accumulated experience of using field indicators by law enforcement and security service employees shows, such a device is applicable for conducting “operational” checks (i.e. unscheduled checks in a limited time before holding important meetings, aniya, etc.) of various objects to identify equipment for unauthorized information transmission. Currently, a large number of different indicator models are presented on the market. At the same time, in our opinion, some issues of the current state and tactical application have not found due reflection in the available literature.
The simplest field indicator (FI) consists of an antenna, a broadband amplifier and a signal level indicator (Fig. 1). The operating frequency range of such an indicator is determined by the bandwidth of the broadband amplifier. Since the PI does not have input signal selection circuits, the PI is not able to scan the frequency range and responds to the appearance of signals from radio eavesdropping devices (ED) almost instantly, regardless of the transmission frequency. But due to the fact that the PI bandwidth is usually several GHz, the sensitivity of such devices is several mV, from 1 to 10, due to which the detection range of the ED is low — in practice, it is a few meters («near zone») and strongly depends on the operating frequency and power of the ED. Basically, this property of the PI determined the order of search activities.
Fig. 1. Block diagram of the electromagnetic radiation indicator:
ШУ – broadband amplifier;
ПУ – threshold device;
УИ – indication device;
АТТ – attenuator;
Сале – level indication device;
Д – demodulator;
УЛЧ – low-frequency amplifier;
Freq – frequency meter
As is known, the principle of detecting a ZU using an IP is based on detecting the fact of exceeding the electromagnetic field level at the receiving point, caused by the appearance of a radio signal from the ZU. The excess level is registered relative to a certain pre-set level (sensitivity threshold, hereinafter referred to as threshold). The threshold is selected manually, in some models of the IP automatically (ST-006, ST-007). The choice of threshold is one of the most important tasks in preparing for search activities and, basically, the effectiveness of the search depends on its choice. The threshold is selected in such a way that the device does not react to the natural level of radiation (background), which is caused by the radiation of office and other remote electronic devices. Moreover, the threshold level should practically coincide with the background level, in this case the device will be on the verge of response and have maximum detection ability. As a rule, with such a threshold level, it is customary to say that the device is adapted to the existing electromagnetic background. A further decrease or increase in the threshold will either cause false alarms of the IP, or will lead to a “coarsening” of the sensitivity, and consequently, to a decrease in the detection range.
Based on the above, it can be understood that the efficiency of the IP strongly depends on the interference environment in a specific search location. In this regard, some models of the IP use rejector or bandpass filters (APP-7). The former significantly reduce the level of interference from known sources (usually TV transmitters) and are tuned to the most powerful of them. The latter narrow the frequency range of the search, and therefore reduce the interference power at the input of the device. Usually, several bandpass filters are used, each of which is tuned to its own frequency range, together they cover the frequency range of the IP and can be used selectively during the search.
As additional features, some IP models use frequency meter and acoustic binding modes. These features have a lesser effect on the search efficiency and are mainly intended for additional identification of the radio signal source in order to determine: dangerous/non-dangerous. Also, recently, more and more models have appeared that can identify known digital communication standards, such as: GSM, DECT, Bluetooth, Wireless Lan protocols (ST-006, ST-007, RICH-3, Obereg). With the advent of chargers that use high-tech information transfer protocols, this is especially relevant.
The frequency meter mode allows you to measure the carrier frequency of a radio signal, the level of which significantly exceeds the background level. This makes it possible to initially identify the transmitter by the carrier value, and if it is a legal transmitter, it can be considered harmless. The frequency meter mode is also useful when the carrier frequency of a dangerous ZU is known and the task is to finally localize the transmitter of a dangerous ZU. For example, when using automated radio monitoring systems, search and identification can be carried out automatically. In this case, the carrier frequency of the ZU will be determined by the system, and localization is more conveniently carried out using a power supply with a frequency meter mode (ST-007, APP-7, RICH-3, Obereg).
It is known that the acoustic binding mode allows you to evaluate the demodulated signal from the output of the broadband amplifier of the IP by ear. In addition, if the ZU uses a simple modulation method (AM, FM) and the speaker of the IP is located close to the microphone of the ZU, then in most cases we will hear a characteristic whistle of negative acoustic feedback. This mode can also be used for the simplest acoustic control of the ZU, in this case, for more effective listening, it is recommended to use headphones.
Speaking about indication methods, the IP can be divided into two groups: search and threshold. Search IP evaluates the level of exceeding the threshold in some conventional units. This allows searching for the maximum electromagnetic field on the object. The operator moves around the object in search of the maximum level of the electromagnetic field. The indicator device can be a LED segment scale or an LCD display, which displays the quantitative value in numbers, sometimes there are pointer indicators. Level assessment is indispensable when searching for a charger, since only by analyzing the change in the level of the electromagnetic field when moving around the room can we understand whether we are approaching the source of radio emission or moving away. Most IP models use several types of indication in addition to the main type. Often there is a possibility of assessing the signal level by a changing sound tone or by sound clicks with a changing repetition rate.
A threshold detector compares the current level of the electromagnetic field with the threshold and gives a binary answer: YES — exceeded, NO — not exceeded. The scope of application of such detectors is small, since it is difficult to search for a ZU using such devices. Threshold detectors can be used in stationary conditions as guard devices. When any ZU appears on the object, the threshold will be exceeded, which the detector will signal. However, it is worth noting that to monitor large areas, it will be necessary to use several detectors. Some modern models have memory and are able to keep a log of events at the object for further analysis.
In our opinion, it is important to classify the detectors in order to consider and analyze their tactical capabilities. According to their functional purpose, the detectors used can be conditionally divided into three groups: small-sized, search, and camouflaged (Fig. 2).
Fig. 2. Classification of field indicators
Let's analyze the presented classification. Small-sized IPare intended for “simple” monitoring of the electromagnetic environment in a specific location. The area of examination in this case should be small, or the potential carrier of the ZU (the interlocutor or the suspicious object) should be known. Such monitoring using the above-mentioned SP does not require special professional training and can be performed by almost any “user”. The main function of small-sized SP is to turn on the indicator when the electromagnetic field level exceeds a specified threshold. Some small-sized SP have a sensitivity regulator, with the help of which the response threshold is set. Such indicators can be used to detect the ZU in the near zone (within 1 – 2 m). The advantages of such power supplies include their small dimensions and weight. The disadvantages are relatively low technical indicators, as well as the lack of signal source identification modes (acoustic binding, signal level assessment, frequency measurement, etc.), low sensitivity. Small-sized power supplies can be used for “rough” localization of radiation sources.
Camouflaged power suppliesare intended for hidden use. Their main feature is that these devices are made in the form of ordinary objects that are used in everyday activities while maintaining their basic functional capabilities. The use of such indicators does not arouse suspicion. They have fairly high technical characteristics. Some camouflaged IPs have hidden indication (“DI-K”, “Sputnik”). The advantage of camouflaged IPs is the secrecy of use, and the disadvantageis the inability to identify the source of the signal.
Search IP are intended for conducting search activities. Their use requires a certain level of technical training of the “user”,especially for modern power supplies, which have a fairly large number of controls and have wide technical capabilities. Search power supplies have: an acoustic lock mode, a sensitivity regulator, bandpass filters, have high sensitivity, some power supplies have the ability to measure frequency, allow measuring the signal level in the near zone, have a tone indication of the signal level, etc. Thus, professional power supplies have the greatest advantages compared to other types of power supplies. The disadvantage is the high price.
Let us analyze the presented classification. Based on the classification, it follows that the use of search IP, which have a large set of technical characteristics, allow to determine the presence of a ZU in the near zone and localize its location, has a special “tactical” diversity. Let us consider the main tactical issues of searching and localizing a ZU using search IP.
Practice shows that when using IP, two main methods of searching and localizing radio bugs are used separately or in combination — Amplitude method (AM) and the Acoustic binding method(AZ). As is known, AM is based on recording the increase in the level of the received IP signal as the receiving antenna of the device approaches the location of the signal source. The radius of the source detection zone depends on the power of the signal it emits, the directionality of its antenna, and the level of the electric field background at the location of the receiving antenna of the device. The AZ method is based on the occurrence of negative acoustic feedback between the microphone of the radio bug and the speaker of the device. A sign of the occurrence of AZ is the appearance of a characteristic “whistle”, the tone and intensity of which change as the speaker of the device approaches the microphone of the radio bug.
At the same time, a study of the experience of using IP shows that the AZ effect occurs only in relation to the BUG, which uses conventional types of modulation — amplitude and frequency (narrowband or broadband). Moreover, in the case of frequency modulation, the effect is based on the presence of “parasitic” amplitude modulation in the frequency-modulated signal. In the case of a high-quality ZU, for example, a quartz-coated one, the “acoustic binding” effect will be quite weak, up to complete absence. Of particular interest for working with IP, in our opinion, may be the developed and practically tested tactical and technical approaches to conducting a search depending on the type of “searched” ZU.
Since in most cases, when conducting a search for a ZU, radio microphones are detected, let us consider the main tactical features of conducting a search depending on the type of radio microphones detected.
As is known, the main feature of radio microphones with parametric stabilization of the transmitter frequency is the large limits of change of the carrier frequency (up to several megahertz). Taking into account the accumulated experience for detection and localization of this type of memory device, it is most advisable to use both AM and AZ methods with virtually no restrictions.
Radio microphones with quartz frequency stabilization and narrow-band frequency modulationhave small limits of carrier frequency variation (up to tens of kilohertz) and a low level of sound signal at the output of the amplitude detector of the IP receiver, which leads to significantly smaller sizes of the AZ occurrence zone. Therefore, for searching and localizing this type of ZU, it is most advisable to use the amplitude method.
Of particular interest, in our opinion, may be the developed tactical options for conducting search activities using IP to detect professional means of covertly obtaining information — namely radio microphones with an external transmitter and radio microphones with a closed or masked radio channel.It should be noted immediately that the search for professional ZU is highly complex and requires an expansion of the range of technical means used to identify ZU. Nevertheless, with a certain degree of probability, there are some tactical possibilities for detecting such ZU. Let's consider them briefly.
As is known, the main feature of radio microphones with an external transmitter is the separation of the microphone installation locations and the radio transmitter itself (up to moving it to another room). Experience shows that in this case, when conducting a search, a combination of the AZ and AM methods is necessary. Moreover, to localize the microphone, it is necessary to use the AZ method, and to search for the radio transmitter (in the room being checked or outside it) — AM.
Professional means of covertly obtaining information include radio microphones with a closed or masked radio channel.Experience shows that when searching for such means, the main feature is that the received and demodulated signal of the IP does not carry information about the acoustic background of the room, which makes it impossible to carry out audio monitoring of the ZU. This is determined by the use of spectrum inversion methods, digital transmission methods and complex types of modulation in these microphones to close (mask) the radio channel. Therefore, for their detection and localization using the IP, there is only one tactical method — the use of AM. To increase the reliability of such detection, it is necessary to supplement it with an analysis of oscillograms and spectrograms of the “dangerous” signal being investigated and, accordingly, to expand the range of technical means used.
In general, the tactics of detecting radio microphones using the IP are well-developed and consist of a systematic and thorough walk around the controlled object, moving along the walls, as well as examining the furniture and other objects located in it. When walking around, the IP antenna must be oriented in different planes, making smooth, slow turns of the main unit and achieving the maximum signal level. It is advisable to keep the IP antenna at a distance of no more than 20 — 25 cm from the surfaces and objects being examined. If there are no restrictions on the use of the AZ method, the speaker of the built-in loudspeaker of the IP should be oriented towards the surfaces and objects being examined. When the device antenna approaches the location of the ZU, the electromagnetic field strength increases, and the signal level at its input increases accordingly. For visual indicators — when the set threshold signal level is exceeded, the number of colored sectors of the level indicators increases (or the readings of the pointer indicators increase), for sound indicators the sound signal level increases (or the frequency of sound alarm clicks increases).
When using the AZ mode, by reducing the dynamic range of volume and increasing the response threshold, you can narrow the inspection zone and thereby localize the installation location of the charger with an error of 10 — 15 cm. Additional opportunities, primarily for classifying radio emissions, are provided by periodically switching on the demodulated signal listening mode in the IP.
As the study of the practice of using IP shows, in the case of conducting search activities to detect a charger with a masked radio channel, an additional tactical technique that increases the efficiency of the search may be the creation (and, accordingly, listening using IP in the audio control mode) of an acoustic background (a clap, a blow on a table top or a metal object, the use of various household sound sources) in the room being checked.
Of certain practical interest is the use of IP to search for “network” radio microphones(powered by a 220 V network). In general, the tactics of searching for “network” radio microphones and localizing their installation locations are carried out using the same methods described above. To activate them, it is necessary to turn on a test sound source and, using the IP, check the probable hiding places of “network” chargers using the previously discussed methods. As experience shows, probable hiding places of such chargers are usually located in sockets and switches. When searching for “network” chargers, household electrical appliances located in the monitored room must be checked. To do this, it is necessary to turn on the available lighting devices with incandescent lamps one by one and connect the power cords of household appliances to the power outlets. Each of the newly connected devices is examined sequentially.
In our opinion, the use of search IP for searching telephone radio repeaters (TRR) can also be of great practical interest. As the analysis of practice shows, according to the statistics of detection, TRRs are in second place after radio microphones. Searching for TRRs using IPs has certain features. As is known, despite the variety of TRR design options, by the method of connecting them to the elements of the telephone line (TL), it is possible distinguish two groups — with galvanic connection to the TL and contactless connection to the TL. In this case, the galvanic connection of the TRR to the TL can be carried out both in series (in the break of one of the TL wires) and in parallel (simultaneously to two TL wires). TRRs of series connection are distinguished by their main feature — the appearance of an emitted modulated signal on the air only when the telephone receiver is lifted. (I would like this tactical feature of conducting search operations to be taken into account when inspecting the TL). In this case, the signals of the automatic telephone exchange (“call”, “busy”), the clicks of the number dialing, the conversation of subscribers after the connection is established must be clearly heard. Such a TRR can, in principle, be installed on almost any section of the TL. At the same time, as a study of practice shows, the most likely places for installing a TRR are a telephone set, telephone sockets, distribution boxes and boards. In this case, it is most expedient to detect a TRR of this type by AM.This is due to the fact that telephones currently in use have fairly sensitive microphones and often a speakerphone mode. Using the AZ method can lead to false conclusions about the presence of a TPP installed in the telephone.
Parallel-connected TPPs can have two varieties. The first of them provides for the implementation of only the repeater function.In this case, in the picked-up mode, the signals of the PBX (“call”, “busy”), the clicks of the dialing number and the conversation of subscribers are listened to on the radio frequency. When the receiver is put down, there is no modulation of the radio signal, and the carrier frequency itself may be absent. Such a TRR can be installed in principle on any section of the TL. To localize bugs of this type, AM is preferable with their activation by lifting the receiver of the telephone set.
In the second variety often combine the functions of a TPP, a radio microphone powered by a TL and providing room acoustics control in the on-hook mode. Such bugs are installed on TL elements within the room of interest. To locate them in the on-hook mode, the AZ method is used with a test sound signal. In the off-hook mode, AM is preferable for locating such bugs.
It is necessary to keep in mind that galvanic connection TRRs, as a rule, do not have their own antennas, but use TL wires instead. In this case, the localization of the ZU using the IP can be carried out only by AM by identifying the distribution of the maximums of the high-frequency electromagnetic field along the TL. Taking into account the laws and properties of the electromagnetic field described by Maxwell's equations, the maximums of the high-frequency radiation should alternate after half the wavelength. Accordingly, the closest maximum in relation to the ZU should be removed from it by a distance of a quarter of the wavelength. For example, with a ZU radiation frequency of 300 MHz, the wavelength is 1 meter. Consequently, the radiation maxima for this case will alternate every 0.5 meters, and the most probable places for installing this type of TRR will be located at a distance of 25 centimeters from the maximum points.
TRR without galvanic connection (i.e. inductive information retrieval)can be installed on any section of the telephone line, as a rule, outside the premises of interest on the subscriber wiring without violating the insulation. They form a modulated radio signal only when the telephone handset is lifted. In this case, the signals of the automatic telephone exchange (“call”, “busy”), the clicks of the dialing number, the conversation of subscribers after the connection is established are heard. A study of practice shows that their localization is carried out by AM as the telephone line is examined along its entire accessible length.
The tactics of searching for TRR in general boils down to the following algorithm. First of all, to activate the TRR, it is necessary to lift the telephone handset. The search for the TRR itself is carried out in two stages. First, the telephone sets themselves are checked for the presence of the charger. The radio repeater installed in the set manifests itself in the same way as a radio microphone. When the antenna of the search device approaches such a telephone set, the sound indication means and the visual signal level indicator are triggered. When the device is switched to the acoustic coupling mode, either a continuous or intermittent tone signal of the telephone station is heard in the speaker or in the headphones of the device. In some cases, when the microphone of the telephone handset approaches the speaker of the device, the effect of «acoustic coupling» may occur. It is not recommended to check telephone sets in the speakerphone mode (if provided), since in this case a false «acoustic coupling» may occur between the microphone and the speaker of the device itself.
Next, the search for the TRR is carried out by walking around the premises along the subscriber TL and identifying places with an increase (maximum) in the radio signal level. When walking around, the antenna of the device must be oriented in different planes at the minimum possible distance from the line. It is almost always necessary to check the line up to the main distribution board. Particular attention should be paid to distribution boxes and places where the line is laid with hidden wiring. TRR installed on the line are localized mainly by the amplitude method, supplemented by checking for the occurrence of AZ.
Of practical interest may be the use of IP for detecting radio stethoscopes. As is known, the main feature of radio stethoscopes is that they are installed only on the outside of surfaces enclosing the monitored room, or on pipes of heating systems, water supply systems and other communications extending beyond it. To detect such signals, you can use the audio signal detection mode (by ear), and for localizationsuch ZU — AM with the IP moving (if possible) to adjacent rooms. When searching for radio stethoscopes, it is necessary to inspect all actually accessible external surfaces of the enclosing structures of the room. In addition, since the environment for the propagation of vibroacoustic vibrations can be heating and water supply pipes, these communications are also subject to inspection. As experience shows, in the vast majority of cases, radio stethoscopes use an open radio channel. This makes it possible to analyze the received signal “by ear” in the acoustic control mode. When checking the enclosing structures of the room, the antenna of the search device should be located at the minimum possible distance from the surfaces being inspected, since the radius of the signal detection zone from a radio stethoscope is usually smaller than from radio microphones. When checking pipeline communications, it is necessary to follow the same recommendations, but do not allow the antenna to come into contact with metal surfaces.
Hidden video cameras with a radio channel of information transmission are distinguished by the fact that the signal emitted in the radio range is similar in structure to the signal of the brightness channel of a television broadcast transmitter. Detection of such a signal and localization of its source is most expediently carried out by AM, supplementing this method by listening to the change in the tone of the detected signal and analyzing the change in the signal structure using the appropriate equipment. The tactics of searching for hidden video cameras with a radio channel for transmitting images (often sound) is associated with some difficulties, which are determined by the similarity of the video transmitter signal with the brightness signal of television broadcast transmitters and the operation of a significant number of these devices in the range of television stations (from 60 to 500 MHz). Therefore, in the course of work, upon detection of such a signal, the first task is to recognize its origin — «external/internal». To recognize it, it is necessary to close the windows in the monitored room with curtains or blinds, leaving the interior lighting on. Then it is necessary to turn on and off the artificial lighting several times.If there is a hidden video camera with a radio channel for transmitting images and the audio monitoring mode is enabled, distinct changes in the tone of the detected signal should be heard. If the results of such a check are positive, then the signal can be confidently classified as a “dangerous” signal generated by the video camera transmitter, since changes in the room illumination do not affect the parameters of the television broadcast signal. In principle, video camera transmitters can operate at frequencies up to 2400 MHz. Detection of a signal (similar to a brightness signal) at frequencies outside the television broadcast range almost unambiguously indicates the operation of a hidden video camera transmitter.
It should also be noted that some modern IPs have a communication interface with a PC. This allows storing the accumulated information in a PC for further analysis (ST-007, RICH-3). Basically, the transmitted data are watchdog mode events. Such events include exceeding the electromagnetic field level, the appearance of GSM, DECT transmitters, etc., and the data also records the date, time and duration of the event. Using several such IPs, switching access to them, it is possible to organize the simplest distributed radio monitoring complex with the ability to analyze data. In addition, the ST-007 manufacturers have long announced the future possibility of connecting several remote radio environment analysis modules to one device, and communication with the central device should be carried out via a radio channel. Unfortunately, we have not yet seen practical examples of remote modules. An example of the working window of the ST-007 communication program is shown in Fig. 3.
Fig. 3. Example of the working window of the program for communication with ST-007
Let's consider some fundamental general tactical considerations that must be followed when conducting search activities to detect the previously listed ZU. Among the first features, we can name the mandatory creation of an acoustic background at the control site. Traditionally, such a background is created by installing a test sound source in the controlled room. As such a source, it is better to use a tape recorder with a well-known musical or speech soundtrack.
When analyzing the tactical possibilities of using IP to detect a ZU, it is necessary to note another important feature — covert (or open) search. If there are no restrictions on the covertness of the work (unfortunately, this does not happen often), the previously considered AM and AZ methods are used without any restrictions in accordance with the recommendations presented above. When conducting a covert search using IP, tactical possibilities are sharply narrowed and in this case it is necessary to focus only on AM with listening to detected signals through headphones.
Preparation of the IP itself in general consists of setting the “zero” detection threshold (DT), which is crucial for successful search operations. As is known, the “zero” DT should correspond to the real background of the controlled territory. It should be recognized as tactically important that underestimating the DT leads to frequent false alarms of the IP indication, and overestimating it leads to missing the ZU signal. Both significantly complicate the operator's work, increase the time and reduce the reliability of the test results. Therefore, when setting the “zero” DT value, it is imperative to adhere to several simple and proven rules.
1. Do not install the DT in the premises being checked.
2. Do not allow the use of radio stations, radio telephones and other radio-emitting devices.
3. Do not bring the device antenna close to switched-on personal computers and other office equipment, as sources of EM radiation.
4. Do not allow the IP antenna to come into contact with metal objects and wires, as sources of re-radiated high-frequency signals.
In conclusion, it should be noted that the presented material on the tactical use of IP reflects the current state of the fleet of technical means under consideration. Taking into account the improvement of field indicators, tactical options for their use will also develop, and this must be taken into account.
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