ENSURING THE PROTECTION OF INFORMATION FROM UNINTENDED INFLUENCE BY TECHNICAL MEANS.

• reducing the level of accompanying (undesirable for the RES) radiation by increasing the distance between potentially conflicting technical means;
• separating the coinciding (partially coinciding) spectrum of interfering radiation from the TS and the receptor's susceptibility by a frequency interval that allows their joint operation without reducing the quality of the latter's functioning;
• separation in time of operating intervals of potentially conflicting technical means — use of a common radio resource according to a time schedule.

However, it is quite problematic to solve the problem of ensuring EMC of TS by organizational measures alone, because technical means must be initially ready for operation in the harsh conditions of the modern electromagnetic environment (EMS).

In order to ensure EMC of the TS, the Government of the Russian Federation (RF) establishes a strictly regulated procedure for allocating frequency bands for the operation of RES for various purposes, special conditions for the development, design, construction, acquisition, operation and import from abroad of RES and high-frequency devices (TS), and also determines a set of measures to protect radio reception from industrial (associated) interference. The Government of the Russian Federation reflects its efforts in regulatory documents (for example, RF Government Resolution of 09/08/1997 No. 1142 «On Approval of the Regulation on the Protection of Radio Reception from Industrial Radio Interference»), which are based on legislative acts (for example, RF Law of 02/16/1995 No. 15-FZ «On Communications» or the law «On State Regulation in the Field of Ensuring EMC of TS», which is undergoing approval). In Russia, as in the international community, state (and international) standards are developed and implementedand other normative and technical documents regulating the characteristics of technical means and methods of their measurement. They define the requirements both for the ability of the vehicle to resist and emit interference, and for the conditions of its operation (for example, requirements for the quality of electricity). The technical means must have a certain stabilityto the impact of electromagnetic interference, on the one hand, and to ensure the required limitation of the levels of their accompanying (undesirable for RES) emissions. The development, manufacture, import from abroad, acquisition, sale and use of technical means — high-frequency devices using radio frequencies above 3 kHz, intended for the generation and local use of radio frequency energy (except for use in telecommunications), are carried out only in those radio frequency bands that are allocated for this purpose by the State Commission on Radio Frequencies under the Ministry of Communications and Information of the Russian Federation. At the same time, each technical means manufactured in Russia (imported from abroad) must undergo certificationin the field of ensuring EMC of vehicles in divisions licensed to carry out such work. Based on the results of the research, such a division issues the vehicle manufacturer its EMC certificate andEMC sign.

Before submitting a vehicle for certification, the manufacturer develops and implements technical measures during its production at the design stage, which allow bringing the EMC characteristics of this type of equipment to the values ​​required by state and international regulatory and technical documents. Technical measures are applied for the purpose of:

• reducing the level of accompanying radiation and thereby achieving a reduction in the size of the “interference zone” of the interference source TS;
• reducing the spectrum of accompanying radiation and thereby facilitating more economical use of the frequency resource by these TS.

Among the ways to solve the problem of EMC of TS by technical measures, the following can be distinguished:

• shielding– surrounding either the source of the interfering EMF, or, more often in practice, the receptor, with a casing made of a metal alloy, the composition of which depends on what is to be protected and what type of field the protection is being built against;
• filtration – creating filters on the path of the propagation of parasitic currents that cause accompanying (undesirable for the RES) radiation, eliminating (reducing to an acceptable level) the appearance of interfering interference;
• grounding– an event aimed at ensuring the flow of parasitic currents generated on screens, the housing and other general circuit connections of a technical device into the ground, thereby eliminating the accumulation of potential to dangerous (including for humans) limits.

The tasks of manufacturing and equipping TS with screens are quite complex in calculations and execution technology and therefore, as a rule, are not solved in the process of using TS. However, the user needs to know the role and importance of these devices, when selecting and installing cable equipment and TS during the creation (modernization) of the protected information processing system, as well as during local repairs, not to neglect their installation. Shielding in EMC and information protection tasks mainly involves protecting information lines and TS from interference caused by external random electric and magnetic fields. At the same time, shielding of cable lines also helps to reduce the level of EMF field strength created by communication and power lines in the surrounding space, but this function is less significant, since the voltage and current values ​​​​in the lines are insignificant, and mutual influence is eliminated during their installation at the stage of assembling the entire system. To achieve this goal, it is necessary to adhere to the following recommendations:

When selecting equipment:

a) preference in selecting cable equipment and TS should be given to:

• technical means that have lower levels of EMF emitted into the surrounding space or transmitted to external cable lines (including the power supply network);
• cables with a shielding sheath (coaxial cable), such as bifilar (“twisted pair”) or trifilar (three twisted wires, one of which is used as a shield), triaxial cable (coaxial cable placed in an additional shielding sheath) or shielded flat cable [3];
• fiber optic cables that do not emit EMF and are not susceptible to them.

b) When installing (upgrading) a system for processing protected information:

• the most cost-effective method is group shielding of information lines with a cable shielding box;
• the intersection of cable lines should be carried out at a right angle without physical contact of their shielding shells;
• power and information cables should have a mutual spacing of at least 30 cm when running in parallel (their joint placement in one shielding box is highly undesirable);
• power cables are recommended to be located closer to elements of heating, water supply and ventilation systems (life support) and the building structure, which “absorb” part of the EMF emitted by them;
• information lines must be removed from life support elements and the building structure by at least 30 cm when laid; if they need to intersect, the angle must be right, and the cable shielding must not have physical contact with it.

c) When repairing equipment:

• during installation, the screen must have tight (preferably soldered) contact with the housing bus, which in turn must be grounded;
• the screen casing must not have any cracks, holes, or other damage to its integrity that were formed arbitrarily during repair, other than those provided for during its production;
• the occurrence of an unacceptable level of interference during the operation of the vehicle after repair emphasizes the insufficiently thorough performance of the receptor (or interference source) shielding after repair.

Shielding is practically not performed without ensuring the filtration of incoming (outgoing) conductors. Fig. 3 shows an example of the use of an EMI source shield as part of a vehicle in combination with a power supply filter.

Fig. 3. Shielding of the electromagnetic interference source using a power supply filter:
a – interference source without a shield;
b – interference source in the shield

The tasks of ensuring sufficient filtering in technical means can be implemented separately from screens. They are also complex in calculations and execution technology and are not solved in the process of using the TS. Filtering in a technical means is carried out to exclude the impact of external EMF on the receptor along all connections and inputs, as well as to protect cable lines from interference generated by the means itself. In addition, filters are provided to exclude interference in power supply, control, monitoring and switching circuits. An example of this fact is the protection of a computer from various types of interference in power supply circuits using a network filter. The filter is usually an L-, T- or U-shaped LC— links included in the break of the phase and neutral wires of the power supply network. In any case, the correct use of filtering devices when installing the equipment of the system that processes the protected information will prevent its distortion or loss when exposed to EMF. An example of such a solution is [4], which describes the impact of a broadcast radio station at a frequency of 1.6 MHz on the internal cable equipment of a company. The solution to the problem consisted in installing two specially selected filters on the information lines. The solution diagram is shown in Fig. 4.

Fig. 4. Scheme of application of radio frequency filters,
increasing the resistance of the cable system
to the impact of external electromagnetic interference (option)

The user of the technical device is responsible for solving the problem of constructing the correct grounding of the technical device during installation and operation. According to the international standard, the household power supply network, in addition to the usual “phase” and “zero” wires for the Russian network, contains a third “ground” wire, which is the ground for household TS. The absence of a “ground” wire in the power supply network of our country determines the need for the user of the TS to independently organize proper grounding.

Grounding technology uses grounding electrodes, which are understood as metal electrodes of any shape (pipe, rod, sheet, etc.) located directly in the ground and having electrical contact with it of a certain resistance (the lower it is, the more effective the grounding). The quality of grounding depends on the number of grounding electrodes, the area of ​​their contact with the ground, the final resistance equal to the sum of the electrical resistances of the wires leading from the technical means, the transition contact between the grounding electrodes and the ground, as well as the resistance to the spreading of currents in the adjacent soil layers. The latter depends on the conductivity of the soil, the design of the grounding electrodes and their location (the effectiveness of grounding increases when the soil is moistened with a saline solution). Common deficiencies that lead to the appearance of interfering interference in grounding circuits are cases when:

• different technical equipment is grounded by a common conductor to the grounding bus;
• closed loops are formed in the grounding circuits, common to different connected technical equipment, and others.

General recommendations for organizing the grounding of vehicles in order to reduce interference can be:

• the active and inductive resistance of the connecting conductors must be minimal, for which their length must be as short as possible, and their cross-section as large as possible (for the ground bus, a metal strip with a cross-section of at least 16 mm2 is recommended, and for connecting conductors — a copper wire (“rope”) with a cross-section of at least 4 mm2);
• electrical connections at all contact points must ensure its minimum resistance, taking into account climatic and other destabilizing factors (the presence of loose contact at significant current values ​​can lead to the appearance of contact interference);
• when constructing grounding, it is necessary to minimize the number of common conductors for technical means and circuits in the system;
• when shielding the electric field at low frequencies, all metal elements of the vehicle structure must be connected to its common body (ground).

Grounding schemes used in practice can be divided into three groups:

• series at one point (Fig. 5a);
• parallel at one point (Fig. 5b);
• multipoint (Fig. 5c).

Fig. 5. Grounding scheme options for groups of technical equipment

The first grounding option is the simplest, but it has the highest level of interference due to currents flowing through common sections of the grounding circuit.

The second scheme does not have this drawback, but requires a large number of long conductors, due to the length of which it is difficult to ensure low grounding resistance.

The multi-point circuit eliminates the disadvantages of the first two options, however, when using it, difficulties may arise with the appearance of resonant interference in the circuit contours. Hybrid circuits are usually used when organizing grounding: at low frequencies, preference is given to a single-point circuit, and at higher frequencies, to a multi-point circuit.

There are some peculiarities in the grounding of information cables [5]. The fact is that at high frequencies a wire with an ungrounded shielding shell does not give the required effect. Because the same current flows along the outer side of the shell as along the central conductor (Fig. 6a). Grounding the cable shell at any point shields it from the electric field, and the connection must be made by direct physical contact (preferably by soldering) (Fig. 6b). Maximum shielding of the information cable is achieved if its shell is grounded at several points (Fig. 6c). The use of a bifilar (Fig. 6g) or trifilar (Fig. 6d — 6z) as an information cable significantly increases the stability of the cable system to external EMF. In Fig. 6 shows, as an example, various options for implementing grounding of the information line between the TS, as well as relative values ​​of the shielding efficiency from the effects of the magnetic field (at a frequency of 100 MHz) normalized to the value of its attenuation in the first option.

For long information cables, it is recommended to ground their shield every 0.05…0.1 wavelength of the expected interference [5].

a) 0 dB strong>	b) -2 dB
c) -5 dB	d) -49 dB
d) -57 dB	e) -64 dB
g) -64 dB	h) -71 dB

Fig. 6. Options for data cable grounding schemes

In conclusion, it should be noted that the implementation of the above recommendations for ensuring EMC of the vehicle and cable equipment of the system processing the protected information significantly increases its immunity to EMF and thereby helps protect information from unintentional impact. At the same time, solving the problem of ensuring EMC of the vehicle is a multifaceted collective task that is solved jointly by all interested users of the vehicle in a given area. A large group of technical means used in the industrial and household spheres of a person does not require separate approvals for ensuring their EMC in government agencies if they have an EMC sign and certificate, and the user follows all recommendations during their installation and operation. However, in accordance with the Decree of the Government of the Russian Federation dated 25.12.2000 No. 1002 «On the State Radio Frequency Service under the Ministry of the Russian Federation for Communications and Information», a state structure was formed, which, since April 1, 2001, is the legal successor of the State Supervision Service for Communications in the Russian Federation. It is designed to perform control functions, including identifying vehicles that interfere with the surrounding electromagnetic environment as a result of improper operation or after poor-quality repairs. In addition, it is designed to take measures on applications about the interfering effect of external electromagnetic fields in the radio frequency range on the operation of vehicles. Detection of the fact of operation of a vehicle whose EMC parameters do not meet the requirements of state standards entails its exclusion from operation, and in the event of a repeated event, it implies administrative, and in aggravating circumstances — legal liability.

• GOST R 50922-96 Information security. Basic terms and definitions.
• GOST R 50397-92 Electromagnetic compatibility of radio-electronic equipment. Terms and definitions.
• Gurevich I.S. Protection of computers from external interference – Moscow: Energoatomizdat, 1984. –224 p.
• George Georgevits Twisted pair and radio frequency interference//Networks and communication systems, No. 2, 2001, P28-31.
• Fundamentals of ensuring EMC of radio electronic means /V.R. Vakhlakov, A.G. Rozhkov, B.V. Sosunov, V.P. Chernoles, et al. St. Petersburg: VAS, 1991, 207 p.