Portable system for radio monitoring and determining the location of radio emission sources..
ASHIKHMIN Aleksandr Vladimirovich, Candidate of Technical Sciences
KOZMIN Vladimir Alekseevich, Candidate of Technical Sciences, Associate Professor
REMBOVSKY Yuri Anatolyevich, Candidate of Physical and Mathematical Sciences
Portable system for radio monitoring and determining the location of radio emission sources
This work continues [1] a series of articles devoted to the creation of new technical means of radio monitoring and direction finding based on hardware modules and small-sized digital radio receivers of the “ARGAMAK” series.
The task of determining the location of radio emission sources (RIS) does not lose its relevance and is necessary for the detection and localization of unlicensed RIS, for military purposes, for the fight against terrorism and some other purposes. This task is solved at any time of the year and in any situation, both in urban conditions and outside them in rugged terrain. In the latter case, such indicators of the RIS location determination system as its weight, dimensions, and deployment speed are of particular importance. The creation of such systems has become especially productive after the development of a new family of hardware modules and small-sized digital radio receivers of the “ARGAMAK” series.
This article discusses the general principles of constructing territorially distributed radio monitoring and location determination systems ARC-POM1, ARC-POM2 and ARC-POM3, design features and technical data of radio direction finders included in the system, and also describes the features of organizing control of the ARC-POM3 system using low-speed radio modems and operating modes of the system software.
Radio monitoring and location determination systems for transmitters ARC-POM1 and ARC-POM2
To determine the location of the radio transmitters, differential-range and angle-measuring systems can be used. Currently, angle-measuring systems have become the most widespread, since the organization of a system of several posts for determining the location of radio transmitters is achieved in them by simpler technical means [2].
As is known, with the help of one stationary direction finder it is possible to determine only the azimuth of the direction to the source of radio emission. To determine the location of the IRES it is necessary to have at least two direction finders, removed from each other at a sufficient distance. When determining the location of permanently or periodically operating sources, it is possible to get by with one mobile direction finder, which, while moving, uses any of the three direction finding methods: drive, quasi-stationary method or the method of automatic detection of sources in motion [2]. The situation is more difficult with the direction finding of radio emission sources that operate in covert mode. The operating sessions of such IRES do not exceed several seconds and are often one-time. To determine the location of such sources it is necessary to have a mode of simultaneous or even synchronous direction finding, which is implemented in the direction finding and location determination systems of the stationary ARK-POM1 or mobile ARK-POM2.
The ARK-POM1 system has peripheral stationary direction-finding posts (Fig. 1), including means of communication with the central post of the system. In addition to direction-finding, the central post of the system also performs the function of controlling the entire system and mapping the results of work. To solve this problem, the central post has equipment for controlling other posts of the system. The system may also include a mobile radio monitoring and direction-finding station ARGUMENT, equipped with a navigation system and means of communication with the central post.
The ARK-MK4 [4] radio direction finders, which are part of the ARK-POM1 system, have high tactical and technical indicators. Thus, when using fourth-generation radio receivers ARK-CT3, the direction finder's operating frequency range is from 25 to 3000 MHz. The field sensitivity in the middle of the operating range from 100 to 1000 MHz is no more than 5 μV/m, and at the edges of the range no more than 25 μV/m. The direction finding accuracy is no worse than 30 with a typical value of 1.50, the dynamic range for third-order intermodulation is at least 70 dB. The speed of multichannel direction finding of radio sources, with a signal level at the sensitivity level, is at least 200 MHz/s.
Data exchange between stationary posts of the system is carried out via high-speed radio channels. Modern high-speed radio data transmission systems operate in the microwave range and provide data transmission speeds of 10 Mbit/s and higher. When using directional antennas, typical distances between posts are 10 – 15 km.
For data exchange with a mobile station, such high-speed systems are practically unusable due to the lack of direct visibility and the need to use directional antennas, so low-speed radio communication systems are used here: narrowband radio modems with a data transfer rate of 1200 to 19200 bits/s or radio modems for cellular radio communication of the GSM standard. The low throughput of such radio modems imposes certain restrictions on the volume of data transmitted.
Fig. 1. ARK-POM1 system for radio monitoring and determination of the location of IRI
The ARK-POM2 mobile system, mounted on vehicles (Fig. 2), has relatively weak restrictions on weight, dimensions and power supply system; it uses the same deployable ARK-MK4 direction finders as the stationary system, so the technical characteristics of a single post are practically not inferior to the stationary system. However, low-speed radio communication systems have to be used for data exchange, so special modes of operation with limited traffic are provided.
Fig. 2. ARK-POM2 mobile system for radio monitoring and determination of the location of radio sources
Thus, the ARC-POM1 and ARC-POM2 detection systems can be used to determine the location of radio transmitters, including those that go on the air for a short time. The disadvantages of these systems include their relatively large dimensions and heavy weight, which determines their limited applicability in the absence of roads, as well as in cases where the use of a transport base capable of carrying equipment is undesirable or impossible.
ARC-POM3 Automated Radio Monitoring and Transmitter Location System
The ARK-POM3 automated radio monitoring and transmitter location system belongs to a family of portable multifunctional devices designed for manual transportation by operators. Such devices can be used at stationary or temporary posts, equipped or not equipped with power supply, as well as in open areas.
The ARC-POM3 system is designed for radio monitoring, simultaneous direction finding and determination of the location of radio emission sources. It consists of a central post and one or two peripheral posts, as shown in Fig. 3. Each post in the system can function both as part of the radio emission source location system and independently.
Fig. 3. Portable ARC-POM3 radio monitoring
and radio emission source location system
The structural diagram of the central post equipment is shown in Fig. 4.
Figure 4. Structural diagram of the equipment of the central post of the ARK-POM3 system
The central post includes:
- A portable panoramic radio direction finder, consisting of a deployable antenna system and a two-channel digital radio receiver.
- A data transmission system, including a radio modem with an antenna.
- Power supply system.
- Personal computer (PC) of the Notebook type with software and electronic digital maps of the area.
- Cartography and navigation device ARK-KN1, providing determination of the geographic coordinates of the post and the direction to the north.
There are two options for organizing peripheral posts.
The first option — the composition of the peripheral post coincides with the composition of the central post. In this case, the post operates under the control of a personal computer and is capable of performing the entire possible set of radio monitoring and direction finding functions, like the central post.
The second option — the personal computer is not included in the peripheral post. In this case, the narrowband radio modem is connected directly to the analog-to-digital processing unit. The post operates under the control of the internal firmware of the unit. Such a solution has its advantages and disadvantages. The advantages include:
- the complexity of operating a peripheral post is reduced due to the absence of a personal computer in its composition, which usually operates in a narrow range of ambient temperature and humidity;
- the energy consumption of the post equipment is reduced;
- the portability and deployment of the post is simplified;
- the requirements for the qualifications of the service personnel are reduced.
The disadvantages of the second option include:
- limited number of functions performed, since the equipment is controlled by firmware;
- the need to use narrowband radio modems controlled via the RS-232 protocol;
- in the event of a failure of the central post, the peripheral post will not be able to assume its functions.
Which of the two options is preferable is determined by the specifics of the system's operation in each specific case.
Features of the design of a radio direction finder
As in many modern automatic systems, the ARK-POM3 location system uses the correlation-interferometric direction finding method [4]. The advantages of this method include, firstly, the ability to take direction finding of virtually any type of radio signal, including broadband signals with complex types of modulation. Secondly, the ability to process and distinguish two or more signals simultaneously in one frequency channel, both in the case of multipath reception of radiation from the same source and in the reception of radio signals from several sources with overlapping spectra. Thirdly, this method has a wide range of operating frequencies and the ability to take direction finding both in azimuth and in elevation.
The post includes a folding antenna system AC-MK7M, designed for installation on a collapsible mast up to 4 m long. The antenna system has an operating frequency range from 25 to 1000 MHz, in this range its parameters are not inferior to the parameters of AC-MK4. The hinged fastening of the antenna elements and rotating crossbars significantly speed up the deployment of the system. Deployment of the antenna system comes down to fixing it on the mast tail until the transverse holes of the antenna mounting socket and the mast tail are aligned, fixing the antenna on the mast with a locking pin, turning the antenna crossbars by 900 until they are fixed on the base of the block. In this case, the antenna elements always maintain a vertical position, as shown in photo 1.
Photo 1. Deployment of the ARK-MK7M antenna system
During transportation, the antenna system is folded and placed in a hard case equipped with carrying straps (photo 2). When folded, the diameter of the antenna system is 480 mm.
Photo 2. Placing the AC-MK7M antenna system in a carrying case
Photo 3. Two-channel signal converter in a protective casing
Photo 4. External view of the analog-digital processing unit ARK-ATS-MK7
Until 2005, the direction finding posts of the ARK-POM3 system were equipped with a third-generation CRPU consisting of a two-channel signal converter and a two-channel analog-to-digital processing unit (ADPU), located separately from each other (photo 3, 4). In this case, the signal from the antenna system at a radio frequency via a lowering cable goes to the input of the two-channel signal converter, located in a protective casing on the first link of the mast under the antenna system (photo 1). The casing is equipped with a forced ventilation and heating system to ensure operation of the equipment in the temperature range from -500 C to +500 C.
In turn, the signal from the converter to the two-channel analog-to-digital processing unit is transmitted at a relatively low intermediate frequency, which reduces losses in the connecting cable and reduces its antenna effect. Placing the converter near the antenna system makes it possible to move it to an elevated location using a connecting cable up to several hundred meters long from the operator's workplace.
The two-channel analog-to-digital processing unit (ADPU) ARK-ADPU-MK7, which is part of the post, is shown in Photo 4, and its structural diagram is in Fig. 5. ADPU converts a pair of analog intermediate frequency signals arriving at inputs A1 and A2 into digital form. Output A3 is used to control the digital receiver. The digital processing module performs subsequent conversions of digital signals in accordance with the spectral analysis and direction finding algorithms. ADPU also includes a digital demodulator designed to demodulate signals with frequency, amplitude and angle modulation.
Fig. 5. Structural diagram of the analog-to-digital processing unit ARK-ATS-MK7
The analog-to-digital processing unit can operate in two modes: in automated mode under PC control and in autonomous mode without PC.
In the automated mode, control from the PC is carried out using the special mathematical software package SMO-PPK (Fig. 6). This package allows you to solve all the main tasks of radio monitoring, including studying the radio range load, searching for new radio signals, detecting active radio channels in a given range or list of frequencies, single-channel and multi-channel direction finding, and evaluating the parameters of radio signals. The tasks of technical and statistical analysis are solved by the software packages SMO-STA and SMO-ASPD, respectively. Finally, the display of bearings and the results of determining the location of the radio source is carried out using the software package SMO-KN «Stalker» (Fig. 7). A separate article will be devoted to a detailed description of the special mathematical software used when working with the complex.
Fig. 6. The SMO-PPK program window in the direction finding mode.
Fig. 7. The SMO-KN program window in the source location determination mode.
If a PC is not connected to the BATSO, after the power supply voltage is turned on, the radio direction finder switches to autonomous operation. Possible modes of autonomous operation are listed in Table 1.
Table 1. Modes of operation of the radio direction finder without a PC
| Mode number | Mode name |
| 0 | Settings |
| 1 | Spectrum in the 2 MHz band |
| 2 | Averaged spectrum in the 2 MHz band |
| 3 | Peak spectrum in 2 MHz band |
| 4 | Spectrum in 0.5 MHz band |
| 5 | Averaged spectrum in 0.5 MHz band |
| 6 | Peak spectrum in 0.5 MHz band |
| 7 | Bearing (according to the selected algorithm) |
| 8 | Diagnostic mode |
| 9 | Radio modem (optional) |
In the autonomous mode, the processing results, bearing, spectrum, correlation curve and other values are displayed on the liquid crystal display (LCD). As an example, Fig. 8, 9 shows the LCD display in the modes “Spectrum in the 0.5 MHz band” and “Bearing”. As we can see, the equipment tuning frequency is 337 MHz, the demodulator of signals with narrow-band frequency modulation (NFM) is turned on, with the band selected for bearing finding of 25 kHz, the azimuth value to the source is 182 degrees.
Fig. 8. Mode “Spectrum in 0.5 MHz band”
Fig. 9. “Peleng” mode
Radio equipment control: selection of mode, frequency, demodulator type, direction finding band is performed using the keyboard on the BACO unit body. In all modes, it is possible to listen to the audio signal at the demodulator output.
When selecting the “Radio modem” mode, the BATSO control firmware checks for the presence of a radio modem connected to the RS-232 port. If a radio modem is detected, the firmware attempts to establish a connection with the central post. In the event of a successful connection with the central post, the peripheral radio direction finder continues to operate according to commands received via the radio channel from the central post.
Since 2005, instead of the ARK-CT2 radio receiver, the direction finding post is equipped with a two-channel digital radio receiver of the ARGAMAK series [1]. This receiver, compared to the ARK-CT2, has a four times smaller weight and five times smaller dimensions, increases the speed of obtaining a bearing panorama to 200 MHz/s or more, expands the frequency range to 3000 MHz, increases the dynamic range for third-order intermodulation to 75 dB and ensures increased reliability. The technical characteristics and design features of this receiver are discussed in detail in [1]. Photo 5 shows the appearance of the single-channel signal converter ARK-PS5.
Photo 5. Single-channel signal converter ARK-PS5
Currently, the development of the AC-MK11 antenna system is being completed for the ARC-POM3 system, which should replace the AC-MK7M antenna system. The new antenna system is structurally combined with a telescopic mast, which significantly reduces the time for its deployment. Despite the fact that a mast has been added to the antenna design, the weight of the packaging for transportation has remained virtually unchanged. The antenna system uses specially designed flat receiving elements, fixed to the base body with rotary crossbars. Flat elements have made it possible to reduce the antenna diameter when folded to 320 mm. When unfolded, the height of the AC-MK11 antenna system is 4 m, with the transport case used as the base of the mast.
In Fig. 10, the AC-MK11 antenna system is shown in the unfolded state, and in Fig. 11, it is folded for transportation. The AC-MK7M antenna system is shown nearby for comparison.
Fig. 10. The ARK-MK11 antenna system in the unfolded state
Fig. 11. Antenna systems AC-MK11 and AC-MK7M in folded state
Two coherently coupled ARK-PS5 signal converters are mounted directly in the housing of the AC-MK11 antenna system base. This solution made it possible to remove high-frequency cables several tens of centimeters long that connected the antenna system switch to the converter inputs when it was previously located at the base of the mast. Due to this, radio signal losses were reduced, especially in the upper part of the operating range. The time for deploying the antenna system was also reduced, since there was no longer any need to attach the converter to the base of the mast and make cable connections to the receiver.
The design of the antenna system provides for the possibility of installing an additional easily removable ring antenna array (RA), expanding the range of operating frequencies of the direction finder from 1 GHz to 3 GHz. The appearance of the antenna system with an additional RA is shown in Fig. 12.
Fig. 12. Antenna system AC-MK11 with additional KAR
for the operating frequency range of 25 – 3000 MHz
Thus, the use of the antenna system AC-MK11 with a built-in two-channel converter ARK-PS5 expands the frequency range of the direction finder to 3 GHz, reduces its weight and dimensions, and shortens the deployment time.
The new modification of the post also has more extensive capabilities for autonomous operation. Along with the “Spectral Analysis”, “Direction Finding” and “Radio Modem” modes, the “Search” and “Scan” modes have appeared, allowing for the rapid detection of active radio signals in a given range or list of frequencies. After detecting an active radio signal, its spectral analysis or direction finding of the signal source can be performed.
Table 2 presents the main tactical and technical characteristics of the direction finding post with the AC-MK11 antenna system.
Table 2. Main tactical and technical characteristics of the direction finding post
| Operating frequency range, MHz | 25 – 3000 |
| Panoramic analysis speed, MHz/s, not less than | 1500 |
| Receiver dynamic range for 3rd and 2nd order intermodulation, dB | 75 |
| Direction finding method | correlation-interferometric |
| Working angle sector | 360° |
| Multichannel direction finding speed, MHz/s, not less than | 200 |
| Spectrum width of the signal being taken | arbitrary |
| Field sensitivity, µV/m | 2 – 25 |
| Instrumental accuracy (RMS), | 1° – 3° |
| Channel switching speed chan/s | 200 |
| Sensitivity, µV | 1 – 2 |
| Types of recorded information | bearing, spectrogram, time, coordinates, demodulated signal |
| Bandwidth of processed frequencies/resolution in technical analysis | 5 MHz/7 kHz, 250 kHz/500 Hz, 15 kHz/50 Hz |
| Weight of the AC-MK11 antenna system with a built-in digital receiver and protective casing, kg | 14 |
| Weight of the ARC-ATS0-MK7 BACO, kg | 1.7 |
| Weight of the T-96SR radio modem in a protective casing, kg | 1.4 |
| Weight of the cable for connecting the ARC-MK11 to the ARC-ATS0-MK7, 50 m long, kg | 7.6 |
Using the ARK-RP3 hand-held direction finder as part of the ARK-POM3 system
The accuracy of positioning in open terrain is no worse than 1.5% of the distance to the object. The range of the system is largely determined by the terrain and the power of the radio source. The standard value of the range in open terrain for a 5 W transmitter is 10 — 15 km. Thus, the error in positioning under the most unfavorable conditions does not exceed 150 — 250 meters.
For more accurate determination of the location of radio emission sources, the ARK-POM3 system includes a manual direction finder ARK-RP3 [1]. This direction finder is based on a single-channel radio receiver ARGAMAK. The direction finder uses amplitude and phase methods for determining the direction to the RES. To implement this, the direction finder includes a set consisting of four directional antenna modules, each of which is designed to operate in a specific frequency range. The antenna modules have a frequency overlap coefficient from 2 to 4, and a directional pattern shape close to cardioid. The composition of the direction finder is shown in photo 6.
Photo 6. Manual direction finder ARK-RP3
Photo 7. Direction finding in open mode
Direction finding can be performed in open or covert mode. Covert mode is used if the conditions of the task at hand make it unacceptable to draw attention to the operator's work. Each mode uses its own subset of antenna modules. In open mode, the antenna modules are attached to a special handle equipped with a compass, digital indicator and controls. In open mode, the direction finder allows you to determine the direction of radiation sources in the frequency range from 25 to 3000 MHz. An example of direction finding in open mode is shown in photo 7.
The direction finder is controlled using the included remote control unit, which has a panoramic display. The control unit allows you to tune to the required frequency, perform spectral analysis in the simultaneous analysis band, demodulate and listen to the signal, perform an automated search for radio channels in a given frequency range, and detect active channels according to the frequency list. Tuning to a frequency can also be done using the direction finder's handle controls.
In addition, the option of controlling the manual direction finder from a computer is provided. In this mode, it allows for full-scale radio monitoring in the same volume as the equipment of the ARK-POM3 direction finding posts, with the exception of automatic direction finding. At the same time, the same performance indicators of radio monitoring are provided.
The ARK-RP3 manual direction finder has improved weight and size indicators. It is designed to be carried by one operator and used on the move. The direction finder can be used as part of small mobile groups moving on foot, for more accurate determination of the location of the IRI on the ground.
Table 3. Technical characteristics of the ARK-RP3 hand-held direction finder
| Operating frequency range in reception and direction finding mode, MHz | 25 – 3000 |
| Dynamic range for 3rd and 2nd order intermodulation, dB | 75 |
| Signal level assessment limits (taking into account attenuators), dB | 110 |
| Operating temperature range, °C | -20… +50 |
| Weight of the basic set, kg | 5 |
| Powered by: | |
| — battery, V | 12 |
| — AC mains, V | 90 – 250 |
| — automobile on-board network, V | 9 – 32 |
| Direction finding methods | amplitude, phase |
| Sensitivity in direction finding mode: | |
| — for open bearing finding, µV/m | 20…50 |
| — for covert bearing finding, µV/m | 50…200 |
| Instrumental bearing finding accuracy: | |
| — with open direction finding | 7° – 15° |
| — with hidden direction finding | 10° – 20° |
| Sensitivity in panoramic analysis mode, µV | 1 |
| Bandwidth of simultaneous analysis (with resolution of 12 kHz/3 kHz) | 2 MHz/0.5 MHz |
| Display information: | |
| — bandwidth of displayed frequencies | 2 MHz, 0.5 MHz |
| — spectrum display modes | instantaneous, averaged, accumulated |
| — display of receiver tuning frequency | digital |
| — signal spectrum band indication | digital |
| — signal level display | graphic and digital |
Using an additional mobile direction finder
The ARK-POM3 radio source location system is designed primarily for use in areas difficult to access for vehicles. However, in some cases, a situation may arise where the radio source is on the border or inside a residential area. Therefore, to expand the system's coverage area, it seems advisable to equip one of the posts with the previously developed AC-MK7 antenna system in a local radio-transparent fairing for installation on the roof of a vehicle, which makes it possible to carry out direction finding while moving.
Fig. 13. Determining the location of the IRI using a mobile direction-finding post
The algorithms embedded in the used software package of cartography and navigation ARK-KN “Stalker” [2] allow to determine the location of the IRI quite accurately using only one post installed on the mobile base.
If the search objective is a stationary radio emission source, it makes sense to use the method of automatic calculation of the coordinates of movement. During the movement of the mobile carrier, based on the continuously received bearings, the probability distribution of finding the radio emission source is built on the electronic map. This method is effective even in urban areas with multipath propagation. In addition, it allows for spatial separation of radio transmitters operating on the same frequency.
If the sought radio transmitter is also on a moving carrier, the drive method should be used. Various vehicles with increased cross-country ability, including passenger cars, such as the UAZ-3151, can serve as a mobile base for the direction finding post.
Joint operation of the ARC-POM3 with a radio suppression system
In some cases, it is necessary to block an unauthorized source of radio emission immediately after its detection. However, the time interval from the moment of detection of a radio transmitter to the moment when the transmitter becomes physically accessible may be quite large. The damage caused by the fact of the transmitter operating during this time may be quite significant.
In this regard, it seems advisable to include a radio suppression system in the location determination system. The ARC-POM3 system is compatible with most of the suppression systems currently available on the Russian market.
Conclusion
The ARK-POM3 automated radio monitoring and transmitter location system belongs to the portable family. The deployment of posts of this system is possible in difficult rural, forest and mountainous areas. The equipment of one post of the system is easily transported by two operators.
Despite the improved weight and size parameters, the radio equipment and software of the system have high characteristics in terms of speed, sensitivity, dynamic range and direction finding speed. This makes it possible to use the equipment also at stationary and temporary posts.
Further improvement of the system's performance and expansion of its scope of application are achieved by introducing into its composition the ARK-RP3 manual direction finding equipment and a mobile radio monitoring and direction finding post with a previously created antenna system in a local radio-transparent fairing based on a vehicle with increased cross-country ability.
Joint operation of the ARK-POM3 system with radio suppression equipment is envisaged.
Literature
1. Rembovsky A.M., Ashikhmin A.V., Sergienko A.R., Portable automated radio monitoring equipment./Special equipment, 2004, No. 4, p. 39 – 47.
2. Glaznev A.A., Koz'min V.A., Litvinov G.V., Shadrin I.A. Multistation systems of radio monitoring and determination of location of radio emission sources./Special equipment, 2002, Special issue, pp. 20 – 29.
3. Ashikhmin A.V., Zhukov A.A., Koz'min V.A., Shadrin I.A., Localization of radio emission sources and measurement of field strength using a mobile radio monitoring station./Special equipment, 2003, Special issue, pp. 9 – 18.
4. Rembovsky A.M., Kondrashchenko V.N. Method of direction finding of radio signals and multichannel direction finder. Russian Federation Patent No. 2096797 dated November 20, 1997. with priority from July 4, 1996.