RU2408173C1 - Device for protection of technical facility of information processing against leakage of information along channel of stray electromagnet radiations and pickups in line of transfer of data of local computer networks - Google Patents

Abstract

FIELD: information technologies.

SUBSTANCE: invention may be used to prevent leak of information processed by technical facilities as a result of stray electromagnet radiations and pickups (SERP) along lines of transfer of data of local computer networks (LCN), using twisted pair as the transfer medium. Transformer is arranged with volume short-circuited turn, its primary (1) and secondary (2) windings are wound on separate circular conductors located inside metal sleeves (5, 6) and separated by each other by metal partition (3) connected to busbar of signal grounding of technical facility of information processing. Transformer connection between the primary and secondary windings is done through volume short-circuited turn formed by metal partition (3), metal sleeves (5 and 6), turn (8) passing through geometric centres of primary and secondary windings, nut (9), and simultaneously being electrostatic screen.

EFFECT: improved efficiency of suppression of SERP from technical facilities of information processing in lines of transfer of data of local computer networks (LCN).

6 dwg

Description

The invention relates to the field of radio engineering, in particular to ensuring the electromagnetic compatibility of electronic equipment, and can be used to prevent leakage of information processed by technical means due to spurious electromagnetic radiation and interference (PEMIN) via data lines of local area networks (LAN) using as a transmission medium twisted pair.

The widespread use of network technologies for the exchange of data between devices that are part of automated information processing systems has led to the emergence of additional sources of unintended PEMIN and, accordingly, to a channel for information leakage from LAN data lines. A characteristic development trend of the LAN is an increase in the data transfer rate, which leads to the expansion of the PEMIN spectrum in the high-frequency region. Currently, the most widely used in automated information processing systems are LANs built on the basis of the 100 Base-TX standard of Fast Ethernet technology with information transfer rates of up to 100 Mbit / s using balanced signals. Twisted pair cable with a length of up to 100 m is used as the transmission medium. With this cable length, due to the processes determining the propagation conditions of conductive interference, the effectiveness of typical protection measures designed to suppress PEMIN can significantly decrease (Chester L. Smith. Energy Leakage From LANs. ITEM 1996, p. 156). The use of shielded cable, even with several shielding sheaths, also does not solve the problem (M. Pelt. Electromagnetic protection and grounding. Networks. Network World. 2000. No. 6, p. 52). One of the main reasons is the presence of a significant (from tens to several hundred pF) stray capacitance between the windings of the matching transformers used in 100 Base-TX network adapters. Through it, the radiation of technical means of information processing penetrate the LAN data cable and are emitted quite effectively by it. The use of noise suppression filters in this case is inefficient, since their suppression band should be shifted to the frequency range above 150-200 MHz.

A known method and device for reducing electromagnetic interference and radiation associated with the interfaces of computer networks (US Patent No. 5223806, IPC 7 Н04В 3/28), which consists in the fact that the suppression of PEMIN in the data line is provided through the use of a series-connected filter in the network interface connected to the output of the driver, transformer, the midpoints of the primary and secondary windings of which are connected via capacitors to the signal ground, as well as inductors connected to the terminals of the secondary transformer winding a. The LAN data line connects to the chokes via a shielded connector.

The disadvantage of this technical solution is the relatively low efficiency of suppressing PEMIN in the LAN data line, due to the presence of stray capacitive coupling between the primary and secondary windings of the transformer.

A known method and device for reducing electromagnetic interference and radiation, which consists in the use of isolation transformers (R.Zh. White. Electromagnetic compatibility of electronic devices and unintentional interference. Issue 2. Intra-system interference and methods for their reduction. Translated from English .. M., "Sov. Radio", 1979, p.214). To reduce the capacitive coupling between the windings according to the interference signals in the isolation transformers, an internal screen is used in the form of a grounded foil strip placed between the primary and secondary windings. Using this screen, the interference signal in the primary winding closes to ground. Isolation and shielding means used in isolation transformers provide an increased value of resistance between the windings and create a path from the primary winding to the ground bus with minimal resistance for asymmetric interference. This is achieved due to the high insulation resistance of the corresponding structural elements (~ 10 ⁴ MΩ) and a small amount of capacitance between the windings.

Closest to the technical solution to the claimed invention is, selected as a prototype, a device for protecting a technical means of processing information from information leakage through the PEMIN channel in a LAN data line (B. Shustennan, R. Camer, P. Dolan. Novel Transfonner Shielding Concept Intended for Data Communication. IEEE 1997 International Symposium on Electromagnetic Compatibility. August 18-22, 1997. Austin, Texas, p. 188).

In a typical embodiment, an Ethernet network adapter of standard 100 Base-TX uses a circuit (Fig. 1) containing a transformer 1 on a ring core, the primary winding I of which is connected to the outputs of the driver of the network adapter, to generate linear signals and match the data line on a twisted pair cable and inductors 2, wound together on an annular core and connected to the secondary winding of transformer 1. The transmission line on twisted pair is connected through inductors 2 to the secondary of II transformer 1. In the prototype device , to electrically isolate the circuits and coordinate with the data line, instead of the specified transformer and chokes, a transformer is used on the W-shaped core (figure 2), in which the secondary winding II is wound over the primary I, between the primary I and secondary II windings an electrostatic metal foil shield III connected to the signal ground bus. The primary winding of the transformer I is connected to the outputs of the network adapter driver, the secondary II - to the data line. As a result, by reducing the capacitive coupling between the windings, an increase in the suppression efficiency of PEMIN in the data line by 3-4 dB is achieved in comparison with the typical circuit (Fig. 1).

The disadvantages of the above devices are the relatively low efficiency of suppressing PEMIN and the difficulty of ensuring the required bandwidth of the transformer of this design for data rates of up to 100 Mbit / s and above.

The purpose of the invention is to prevent leakage of information processed by technical means due to PEMIN through LAN data lines using twisted pair as transmission medium.

This goal is achieved by the fact that in the protection device of the technical means of processing information from information leakage through the PEMIN channel in the data line of the local computer network, consisting of a transformer with primary and secondary windings, the primary winding is connected to the driver output of the network adapter of the technical means of information processing, the data transmission line of the LAN, the electrostatic screen made of metal foil located between the primary and secondary windings is connected to the secondary winding, Connected to the signal ground bus of the information processing equipment, according to the invention, the transformer is made with a short-circuited volume coil, the primary and secondary windings being wound on separate ring cores located inside the metal cups and separated from each other by a metal partition, transformer coupling between the primary and secondary windings through a voluminous short-circuited coil formed by a metal partition, metal glasses, wines the volume passing through the geometric centers of the primary and secondary windings, a nut, and at the same time being an electrostatic screen.

Comparative analysis with the prototype shows that in the proposed device, it is new that the transformer is made with a short-circuited volume coil, the primary and secondary windings of which are wound on separate ring cores located inside metal cups and separated from each other by a metal partition connected to the signal ground bus technical means of information processing, transformer communication between the primary and secondary windings is carried out through the bulk short-circuit mentioned coil formed by a metal wall, metallic glasses, screw, passing through the geometrical centers of the primary and secondary windings, a nut, and at the same time being the electrostatic screen.

Thus, the invention meets the criterion of "novelty."

The invention meets the criterion of "inventive step", as for a specialist it clearly does not follow from the prior art.

The invention is “industrially applicable”, as it can be used in various fields of radio engineering.

In Fig.1 shows a diagram of the output stage of a typical embodiment of an Ethernet network adapter standard 100 Base-TX, Fig.2 shows a diagram of a prototype device. Figure 3 shows the design of the proposed device, figure 4 presents a diagram of the proposed device. Figure 5 presents the design of the isolation device in which the proposed device is used, figure 6 - experimental characteristics of the transformer with a short-circuited volume coil.

In the proposed device for protecting a technical means of processing information from information leakage through the PEMIN channel, a transformer with a short-circuited volume coil is used in the LAN data line. A transformer of this type belongs to the class of magnetic transformers with a vortex electric field and is a physical analogue of a conventional electric vortex magnetic field transformer used in the prototype. The design features of a transformer with a short-circuited volume coil: shielding of the windings from the outside with a short-circuited coil and from each other, due to the metal partition, allows minimizing, to a value of less than 0.01 pF, capacitive coupling between the primary and secondary windings and ensuring complete shielding of the transformer. A decrease in capacitive coupling leads to a proportional decrease in the level of PEMIN in the secondary winding of the transformer and, accordingly, in the LAN data line.

The design of the transformer with a short-circuited volume coil (Fig. 3) consists of primary and secondary windings on separate ring cores, 1 and 2, respectively, separated by a metal partition 3, a metal sleeve 4 installed and sealed into the partition 3, metal cups 5 and 6, tubes electrical insulating 7, screw 8, nut 9. In the center of the partition 3 there is a hole in which a sleeve 4 is inserted through which the screw 8 passes. In the partition 3 there are ring grooves on both sides, into which the glasses 4 and 5 are inserted. Width rotochek equal cup wall thickness than is provided by the absence of cracks at the perimeter of the connection between the cups and the baffle. After assembling the transformer, the connection of the screw 8 and the glass 5 is soldered. Electrical insulating tubes 7 provide electrical isolation of the windings 1, 2 of the transformer from the sleeve 4. Transformer communication between the primary and secondary windings is carried out through a volumetric short-circuited turn formed by structural elements: a partition 3, glasses 5 and 6, a screw 8 passing through the geometric centers of the primary and secondary windings, nut 9. At the same time, a short-circuited volume coil serves as an electrostatic screen and is a transformer housing. This ensures complete shielding and galvanic isolation between the primary and secondary windings of the transformer.

In the proposed device (Fig. 4), as well as in the prototype device, the primary winding of the transformer I is connected to the outputs of the network adapter driver, and the LAN data transmission line on a twisted pair is connected to the secondary winding II. Partition III is connected to the signal ground bus of the equipment.

The proposed technical solution is implemented in an isolation device for four duplex LAN data lines of 100 Base-TX standard, in which transformers with a short-circuited volume coil are used. The design of the isolation device is shown in FIG. The device contains eight transformers 1 mounted on a bracket 8 installed in the casing 5, a patch board 3, a board 2 with four RJ-45 connectors, a top 6 and a bottom 7 cover, a harness 4. This device can be used to enter shielded volumes ( shielded racks, shielded rooms, etc.) LAN data lines in which twisted pair cable is used as the signal transmission medium. The metal structural parts of the isolation device and the transformer are made of brass.

Figure 6 presents the experimental characteristics of the transformer with a short-circuited volume coil used in the isolation device:

- curve 1 - amplitude-frequency characteristic of the transformer;

- curve 2 - the efficiency of the suppression of asymmetric interference;

- curve 3 - noise level.

It can be seen from the graph (curve 2) that the efficiency of the suppression of asymmetric interference in the frequency range from 10 kHz to 100 MHz exceeds 95 dB.

The proposed technical solution, in comparison with the prototype, provides higher efficiency of PEMIN suppression in a wide frequency range due to full shielding and galvanic isolation of the primary and secondary transformer windings and the minimum possible capacitive coupling between the primary and secondary transformer windings. The use of ring cores allows to provide the required bandwidth of the transformer.

Claims (1)

The protection device of the technical means of processing information from information leakage through the channel of spurious emissions and interference in the data line of the local area network, consisting of a transformer with primary and secondary windings, the primary winding connected to the driver output of the network adapter of the technical means of information processing, connected to the secondary winding data line of a local area network, an electrostatic screen made of metal foil located between the primary and secondary windings connected to the signal ground bus of the information processing equipment, characterized in that the transformer is made with a short-circuited volume coil, the primary and secondary windings being wound on separate ring cores located inside metal cups and separated from each other by a metal partition, a transformer connection between the primary and secondary windings is carried out through a volumetric short-circuited turn formed by a metal partition, metal with takans, a screw passing through the geometric centers of the primary and secondary windings, a nut and at the same time being an electrostatic screen.

Images