Problems of combating radio-controlled explosive devices.

Problems of combating radio-controlled explosive devices..

 PROBLEMS OF COMBATING RADIO-CONTROLLED EXPLOSIVE DEVICES

In modern Russia, the lives of prominent political figures and leading executives of banking and commercial structures are constantly at risk due to the difficult crime situation. Most security firms, agencies and security services have qualified personnel capable of repelling virtually any type of «visible» threat from terrorists, but they remain powerless against remotely controlled explosive devices. Statistics show that radio lines of explosion control (RUV) are increasingly used by terrorists both in our country and abroad. The advantages of RUV over other methods of controlling sabotage are the ability to position the terrorist controlling the detonation at a sufficient distance from the place where the explosive device is planted, which ensures his safety. At the same time, visual control of the situation around the mined object can be carried out to select the time to detonate the explosive device.

Terrorists try to act covertly whenever possible, without attracting attention to themselves, including when making sabotage and terrorist devices. From this point of view, it is much easier to buy a practically ready-made remote radio control device such as a pager, mobile radio station, telephone radio extender, cell phone, security alarm device with their modification for specific situations of intended use. Obviously, such possibilities do not exclude cases of using RC devices based on specially developed equipment. The relevance of the problem forces us to look for and analyze various methods of counteracting such means of terrorism, including radio engineering methods. The article briefly considers the possibilities of counteracting RC devices, proposes a methodology for assessing the effectiveness of suppression equipment, and presents the results of testing domestic equipment in urban and field conditions.

Characteristics of radio control lines

The structural diagram of the RC device is shown in Fig. 1.

The transmitting part of the RUV consists of a control panel, an encoder that forms a command code, a transmitter with an antenna that generates and emits a radio signal with modulation that carries a command to the receiving part to detonate. The receiving part contains an antenna, a radio signal receiver, a decoder and an actuator, such as an electronic key or electromagnetic relay. The receiver performs primary frequency selection of radio signals and selection of a command signal. The code of the received command is compared in the decoder with the reference code and, if they match, a command is formed that is sent to the actuator. The actuator supplies voltage to the electric blasting circuit of the device, consisting of initiation means (for example, an electric detonator), connecting wires and safety elements (switches, contactors, etc.).

The RWR can be characterized by the following parameters:

• frequency range;
• range of action;
• path losses;
• bandwidth of frequencies and sensitivity of the receiver;
• methods of encoding and modulation of the signal.

The specified parameters of the RWR to a significant extent determine the possibilities of counteracting sabotage actions.

Operating frequencies of the RUV.There is a high probability of using in the RC equipment manufactured by the industry for remote control of various models. The distribution of radio frequencies allocated in different countries for radio control according to the «Radio Regulations» covers sections of the frequency range from 20 to 500 MHz. General-purpose mobile radio stations, paging and cellular communication systems operate in separate frequency sections up to 2000 MHz, which is also allocated for scientific, industrial and medical purposes. At present, the frequency range of 2300-2400 MHz is being intensively developed. The most probable frequency range for RC is the developed range up to 1000 MHz, somewhat less likely at present is the use of an extended range up to 2000 MHz, in the future we should expect an expansion of the RC range to 2500 MHz.

Range of RC.The range of the RUV depends on the energy potential of the transmitter and the sensitivity of the receiver. The energy potential is the product of the power values ​​of the transmitter output amplifier and the gain of the radiating antenna.

In the portable version of the transmitting part, the transmitter output power can be from fractions to units of watts. When giving a command to detonate from a car, a general-purpose car radio station can be used, the output power of which can reach several tens of watts. In this case, the range of the radio station can be significantly greater than for a portable transmitter.

The effective gain of the transmitting and receiving antennas is determined by their design and permissible dimensions. Most antennas used in the RUV are pin antennas and are made in the form of telescopic antennas or wire sections. In most cases, the antenna dimensions do not correspond to 0.25xl, but are significantly shorter, since it is necessary to ensure their concealment. In the frequency range of 20 — 100 MHz, the antenna dimensions are no more than (0.05-0.1)xl, which determines their low efficiency. In a higher frequency range, the antenna dimensions approach 0.25xl, and at frequencies of 200 — 500 MHz, loop antennas with turn dimensions of about 25×50 mm can be used. Non-optimal antenna dimensions lead to the fact that their effective gain is no more than minus 6 dB.

Losses on the route.Signal power losses on the route can be divided into polarization and range losses. Polarization losses are caused by non-optimal placement of the emitting and receiving antennas relative to each other in order to meet the requirements for the concealment of their placement. In this case, additional losses can be estimated at 3 dB.

In urban conditions, the range of the radio frequency antenna is affected by the types of surrounding buildings and their density. Due to the proximity of the radio frequency antenna propagation path to the earth's surface, the signal power decreases proportionally to the 4th power instead of the 2nd power for the case of propagation in free space. This means that when the range is doubled, the losses on the ground change by 12 dB, and in free space only by 6 dB, which is typical for rural areas. For open space, the losses on a 50 m path between isotropic antennas in rural areas at a frequency of 30 MHz are 30 dB and 78 dB at a frequency of 1000 MHz, and for urban conditions these losses increase to values ​​of 46 and 80 dB, respectively. In the city, there are also additional losses caused by complex conditions for radio signal propagation and the influence of various absorbing and reflecting obstacles. The magnitude of these losses depends on the type and thickness of the material of the walls of buildings and structures, and these losses increase with increasing frequency. As a result, doubling the distance leads to a sharper increase in losses by 15-25 dB instead of 12 dB, which is especially evident on routes longer than 50 m. The total losses on the RUV route actually determine the minimum distance from the terrorist to the explosive device.

Bandwidth and sensitivity of the receiver.The RUV can use receivers based on superheterodyne or superregenerative circuits. The latter have high sensitivity, but are somewhat inferior to superheterodyne in terms of bandwidth, noise levels and operational stability, while surpassing them in terms of dimensions, weight and energy consumption. The receiver bandwidths, matched with the spectrum of the command signal, are 5-20 kHz for superheterodyne and 200-300 kHz for superregenerative, and 10-100 Hz for low frequency. The most probable expected value of receiver sensitivity is from 2 to 10 μV at ranges of 100-300 m.

Signal coding and modulation methods.In the RUV, one can expect the use of frequency-modulated and amplitude-keyed signals carrying coded information. Without coding, the radio link will have low immunity to interference, which even at low power can cause premature operation of the actuator. To reduce the likelihood of false triggering of the explosive device, a coded command signal is used. Commands in a simple version can be transmitted as a frequency-keyed parcel with sequential transmission of a code combination of 2-5 frequencies in the range of 1-10 kHz or in the form of a binary code of 8, 12, 16 bits or more. In the receiver, a matched demodulator forms time sequences of synchronizing and code pulses, which are fed to the synchronizer and the coincidence circuit of the decoder. Comparison of the received sequence with the reference code allows us to identify the presence of a true command. The duration of a command transmission can be from 15 ms to 2 s, and more complex options with additional confirmation of the command are not excluded.

Features of electronic suppression of radio-electronic weapons

The conditions of electronic suppression of radio-electronic weapons can be characterized by the following factors:

• uncertainty of the location of the object of suppression;
• uncertainty of the frequency of operation of radio-electronic weapons;
• short-term operation of radio-electronic weapons;
• high cost of the risk of ineffective suppression;
• the danger of electronic suppression of communications equipment.

The uncertainty of location requires the emission of interference in all directions, which determines the need to use non-directional transmitting antennas and ensure high levels of interference power at the antenna input. Narrowing the spatial uncertainty, for example in the case of inspection of suspicious objects whose location is precisely known, allows the use of directional antennas, which provide significantly higher levels of radiated interference power, and therefore increases the reliability of protection of inspection personnel from explosion damage.

The jamming transmitter operator knows only the expected frequency range in which the operating frequency of the jamming device is located, which requires the creation of jamming in the entire frequency range possible for organizing the jamming device. Thus, the jamming is of a barrage nature, which is energetically less advantageous than targeted frequency jamming.

The duration of the RUV operation is determined by the duration of a single command, which can be no more than a few seconds. Consequently, the operator of the jamming transmitter has too little time to intercept the command signal and form a targeted jamming on this frequency. It follows that when suppressing the RUV electronically, it is necessary to focus on the continuous emission of a broadband barrage jamming. If there is operational information about the RUV frequency, it is possible to use a targeted jamming frequency with higher efficiency.

A radio-controlled explosive device is designed primarily to affect people. In such situations, even a small price of risk may be unjustified. Therefore, the emitted interference must effectively neutralize the RCV and the operator of the jamming equipment must take all measures to correctly and effectively use the equipment.

The operating frequencies of the jamming transmitters lie in the frequency range saturated with communication and broadcasting channels. Therefore, when jamming the jamming transmitters, it is possible to interfere with the operation of these radio channels in a certain area around the jamming equipment. However, the interference will have the main impact on the communication facilities located in the immediate vicinity of the equipment. If it is necessary to ensure radio communication, it is necessary to introduce «transparency windows» into the equipment at communication frequencies, which increases the cost of the jamming equipment. In some foreign jamming transmitters, tunable rejection filters supplied as additional modules are used to form «windows». In such a technical solution, the relative width of the «transparency windows» is quite high, about 3.5%, which can reduce the guarantees of suppression of the jamming transmitters, the frequencies of which are close to the communication frequencies. Narrower and programmable «windows» can be obtained by constructing jamming transmitters based on DDS synthesizers.

Radio-electronic suppression of radio-frequency electromagnetic waves

Suppression of the jamming device can be accomplished by disrupting its normal operation, causing a failure to execute the command, or by stimulating premature detonation of the explosive. Premature activation of the explosive device at a safe distance is possible by simulating a command signal in the jamming transmitter (the code or set of codes is known), as well as when the jamming device does not use a coded command signal.

The following can be used to create jamming of the jamming device:

• direct noise jamming transmitters;
• transmitters with noise modulation and/or pseudo-random sequences;
• frequency sweeping jamming transmitters;
• short-term transmitters, including spark transmitters.

Depending on the width of the spectrum of the emitted interference, transmitters are divided into barrier and targeted interference transmitters.

Targeted-barrier interference transmitters emit all their power in a frequency range of several tens of MHz (40-80 MHz). The central frequency of such interference can be set in any sections of the entire possible frequency range. There can be several such interference bands and they should be located in the most dangerous sections of the frequency range.

Broadband jamming transmitters emit all the power they have over the entire specified range. The carrier frequency used by the terrorist and the type of his equipment are not taken into account in this case. The main disadvantages are the possible disruption of communication channels in conditions of interference of all frequencies and a decrease in the protection range, since the power of the jamming transmitter is distributed over a wide frequency range. However, broadband jamming makes it difficult for a terrorist to find free frequency areas to select the operating frequencies of the jammer.

Aimed jamming has a significant energy gain compared to barrage jamming, but its implementation requires information about the frequency value at which the jammed electronic device operates. Obtaining such information is associated with time expenditures on detecting a dangerous signal and measuring its frequency. Therefore, for suppressing radio electronic devices, frequency-targeted jamming transmitters cannot be used due to the transience of the electronic conflict between attack and defense means.

Due to the variety of modulation and coding types that can be used in the RCV, a universal interference structure that ensures the neutralization of detonation commands will be interference in the form of white noise, which, in order to reliably block the RCV receiver, must provide the required threshold interference/signal ratio at the input of the suppressed receiver. The advantage of noise interference is its invariance with respect to any type of coded signal and that it cannot cause a false alarm when using a coded signal in the RCV. It can be formed by generating broadband noise in the entire specified frequency band or by modulating the signal generated in the specified frequency band with noise.

With fast frequency sweeping of such a signal, it is possible to provide an interference effect close to the effect of white noise. To ensure this, it is necessary to optimally select the parameters and frequency range of the sweep. Frequency sweep jamming systems are capable of combining the advantages of targeted jamming and can reduce its disadvantages by electronic frequency tuning over the entire specified range, thereby creating interference at all frequencies. In this case, at any given time, interference is created only at one frequency, and all other frequencies in the range are free of interference. Therefore, to ensure the effectiveness of suppression of most radio interference devices, it is necessary to satisfy conflicting requirements for the frequency tuning period over the entire range and the time between the effects of interference on the suppressed receiver.

A radio electronic interference transmitter can be simplified as a series-connected broadband jamming signal generator, a broadband power amplifier and an antenna system, as shown in Fig. 2.

The jamming signal generator is the most complex part of the jamming transmitter. It is implemented on a promising analog and digital element base, which allows not only to monitor the functioning of the transmitter using digital control, but also to quickly change the parameters and modes of jamming by rebooting the built-in processor via a standard interface from a personal computer. The generated jamming signal is amplified to the required power level and emitted by the antenna system.

Considering the high degree of interference broadband, multi-channel design is typical for transmitters. This is primarily due to the difficulties in implementing the antenna system. It is difficult to create a highly efficient antenna of acceptable dimensions that covers a wide frequency range, especially in its low-frequency part. Thus, an antenna in the form of a half-wave vibrator at a frequency of 20 MHz will have a size of 7.5 m, which is unacceptable not only for a portable version of the transmitter, but even for a car one. It is also obvious that it is very difficult to cover the frequency range of 20-500 MHz with one highly efficient antenna and this will require dividing this frequency range into at least two sub-ranges. Moreover, for the lowest frequency range, it will be necessary to create a special antenna that would implement the necessary efficiency and broadband in combination with acceptable dimensions. In this case, losses arising due to non-optimal antenna dimensions and the need to introduce matching devices must be compensated by increasing the power of the interference signal supplied to it.

The number of jammer channels depends not only on the antenna system configuration, but also on the bandwidth of the final power amplifiers. The best solution is for each output amplifier to operate on its own optimized antenna. This design is most suitable for automotive and stationary transmitters. In portable jammers, they usually strive to minimize the number of antennas by using one broadband antenna in the high-frequency part of the operating range (100-1000 MHz) and one antenna in the low-frequency region (20-100 MHz). However, to cover the range from 100 to 1000 MHz, at least two broadband power amplifiers will be required, which, through a frequency-selective combiner, operate on a common antenna.

Radio Electronic Suppression Criteria

The jammer creates a safety zone around itself, which ensures effective suppression of the ECM receiver. Since the RUV and the jamming transmitter usually use omnidirectional antennas, the safety zone in its shape in the azimuthal plane is close to a circle, the center of which coincides with the location of the radio explosive device.

The effectiveness of a jammer can be estimated by the distance from the explosive device placement site to the jammer, at which the radio link is suppressed (the actuator of the jammer does not operate), for a certain specified distance between the control signal transmitter and the placement site. The distance between the receiving part of the jammer and the jammer will be called the protection range Dz, which determines the size of the jammer's safety zone. When the jammer is removed from the placement site at a distance not exceeding the protection range, the terrorist's command does not detonate the warhead of the radio explosive device (Fig. 3). However, almost all advertising materials do not indicate the distance between the control signal transmitter held by the terrorist and the explosive device placement site, which does not allow one to estimate the real effectiveness of a particular jammer. Therefore, it is not possible to use the advertised value of the protection range in practice.

Fig. 3. Determining the protection factor

In real conditions, the distance of a terrorist to the planting site is unknown and can vary widely, and therefore the protection range value that is provided in specific conditions can differ significantly from the value specified in advertising materials. It is proposed to use an objective indicator of protection effectiveness in the form of a relative coefficient equal to

K = Дз/Rт,

where Rт is the maximum distance between a terrorist with the transmitting part of the RUV and the planting site of the receiving part of the RUV for a given Дз value, at which the RUV receiver still does not operate.

The coefficient K is a function of the parameters of the jammer and the RUV and does not depend on their mutual arrangement. For broadband interference and the arrangement of the receiver and jammer antennas near the earth's surface

K = (h PпGпD fпр/a PGD fп)1/4,

where a is the threshold interference/signal ratio at the input of the receiver of the RUV, at which its suppression occurs; PG is the energy potential of the transmitter of the RUV; PпGп is the energy potential of the interference transmitter; h is the quality factor of the interference; D fпр is the effective bandwidth of the linear part of the receiver of the RUV; D fп is the width of the spectrum of the interference signal.

The protection factor will be the greater, the higher the radiated power of the jammer and the narrower the interference spectrum. Using this indicator, for each tactical situation characterized by the minimum distance to which a terrorist can approach the place of sabotage, it is possible to calculate the protection range provided by the jammer. The coefficient K with the same parameters of the jammer allows objectively comparing different types of jammers by the effectiveness of the jammer. Of practical interest is the value of the protection range that is safe for the protected person or object. Obviously, the protection range must exceed the radius of the zone of destruction of the warhead of the radio explosive device.

Thus, when a 200 kg land mine exploded and destroyed a building, car passengers at a distance of 75 m from the explosion site were in practically safe conditions. Cars also protect against excess pressure created by a blast wave. Thus, passengers relatively easily withstood excess pressure of 1.5 psi created by an 80 kg TNT explosion at a distance of 66 m from its epicenter. Powerful and signal charges of directional action with a damaging effect of long range are available only to trained professionals. For other types of charges, the radius of the affected area is determined mainly by the mass of the explosive. The typical range of high explosive destruction with a charge power of 100-500 g of TNT is 2-5 m. Therefore, the minimum protection range should be taken as no less than 10 m, and the maximum no more than 20 m. It is clear that when the terrorist is 50 m away from the explosive device planting site, the protection factor should be no less than 0.2-0.4 depending on the charge power. When the terrorist is 100 m away, a jamming transmitter with a protection factor of 0.1-0.2 can be used.

The coefficient of the protective range of the jammer is usually determined experimentally on samples of the jammer for typical conditions (open terrain, urban development). The efficiency of the portable equipment «Rhodiola» was determined for samples of the jammer in the frequency range of 20-30-1000 MHz with amplitude-keyed, frequency-modulated, coded signals and output powers of up to 0.5 W. During the tests, it was found that the device «Rhodiola» provides effective suppression in urban conditions of jammers with a protection coefficient of at least 0.22, in open terrain the protection coefficient was 0.33.

Energy potential of suppression equipment

From the definition of the protection factor it follows that an increase in the safety zone can be achieved by increasing the energy potential of the jammer, increasing the quality of the jammer and reducing the width of the jammer spectrum. An increase in the quality of the jammer has a physical limit. Therefore, an increase in the safety zone can only be achieved by using a jammer with a higher output power and a higher gain of the transmitting antenna.

An assessment of the energy potential of the equipment for suppressing radio frequency interference shows that in order to ensure a protection factor of 0.2, a jamming transmitter with a minimum integral power of 80-100 W, distributed in a frequency band of 1000 MHz, and 160-200 W in a frequency band of up to 2000 MHz is required.

The magnitude of the interference power that can be generated by the transmitter is limited by the power of the primary power sources. The power of the primary power sources available to portable systems is limited by the capacity of the power batteries, which in turn is limited by physical parameters — the weight and size of the battery. This does not allow for the generation of the required interference power in a wide band of operating frequencies for a sufficient time with acceptable weight and size characteristics of the interference transmitter. Existing batteries with maximum specific characteristics provide for the generation of an output power of 80 W in the frequency range up to 1000 MHz for 30 min. at an ambient temperature of minus 20 °C with the following weight and size characteristics: silver-zinc weighs 4 kg, metal hydride — 8 kg, nickel-cadmium — 12 kg and lead acid — 28 kg. The use of silver-zinc batteries is limited by their high cost. Metal hydride batteries, whose characteristics exceed those of nickel-cadmium batteries, are approximately 1.5 times more expensive. Nickel-cadmium batteries are significantly cheaper and exceed silver-zinc batteries in terms of weight and dimensions by at least twice. Lead-acid batteries are inexpensive, but have unacceptable weight and volume. Therefore, most portable jammers use nickel-cadmium batteries.

To improve the weight characteristics of portable transmitters, it is necessary to use a set of externally connected additional power sources. Thus, primary power sources limit the operating frequency band and output power of most portable jammers. Thus, foreign jammers with an output power of 10-60 W have an operating frequency range of up to 500 MHz (HP — 3035, Vixen ECM — F, Transjam DTY 920). Domestic jamming equipment «Rhodiola» with a radiation power of 70 W provides a frequency range of 20-1000 MHz in a portable version.

The output power of car system transmitters is limited by the power of AC or DC power sources that can be placed in the car. It is possible to use special generators with power take-off from the car engine shaft, while the output integral power of the jammer can reach 300-500 W, but long-term (more than 1 hour) operation is possible only with the car engine running and buffer batteries installed. For example, such a principle is implemented in the foreign car jammer HP — 3260, providing 500 W of power in the frequency range of 20-1000 MHz, as well as in domestic equipment «Saksaul», which in the frequency range of 20-2000 MHz provides a power of 500-1000 W.

Technical characteristics of foreign and domestic radio electronic jamming transmitters are given in Table 1. However, the protection factor for the advertised product samples is not given, which complicates their comparison with each other or the justified choice of a jammer for a specific situation. The authors will be interested in participating in experiments to determine the protection factor of various radio interference generating equipment on a statistically sufficient array of jammer samples.