Panoramic frequency range receivers.
Panoramic frequency range receivers
The most important tasks of ensuring the security of communications and telecommunications:
— search for and detection of electromagnetic signals with unknown parameters and radio interference;
— identification of the type and parameters of modulation of electromagnetic oscillations, demodulation of the information contained in them;
— measurement of the level of spectral components of electromagnetic oscillations;
— measurement of phase-frequency, amplitude-frequency and noise characteristics of receiving and amplifying equipment, parameters of nonlinear distortions in them;
— measurement of parameters of side components of output signals of radio transmitters.
The specified tasks are solved using devices that belong to the class of measuring receivers, spectrum analyzers or frequency range scanners. Among them, frequency range scanners are focused on detecting the presence of a high-frequency signal concentrated in frequency at their input with fairly rough but unambiguous estimates of its average frequency and power. Spectrum analyzers, on the contrary, often ambiguously or inaccurately record the average frequency of the signal, but allow you to establish the shape of its spectrum. Panoramic receivers, unlike spectrum analyzers, have a preliminary selective amplifier. Therefore, their sensitivity is significantly higher, but they are inferior to spectrum analyzers in terms of the time it takes to view the selected range. Measuring panoramic receivers (MPR) include additional means for demodulating some classes of radiation and for accurate measurements of the frequency characteristics of circuit devices and paths in the selected frequency range.
Complex automated devices, which are IPPs, have a significant number of parameters, properties and consumer characteristics. The purpose of this publication is to review the state of the modern market for such products and compare them according to various criteria.
We will limit ourselves to IPPs of the radio frequency range, intended mainly to ensure office security, control the presence and decipher weak radiation from special equipment.
Basic terms and definitions
For each of the above mentioned tasks, certain technical characteristics may be of interest. The following basic parameters are common to all applications:
— range and subranges of operating frequencies;
— resolution;
— sensitivity;
— frequency instability of the reference generator (or several generators with multiple frequency conversion);
— dynamic range of the measured signal level;
— types and parameters of modulation.
Let us briefly consider the definitions and methods of standardizing these parameters.
Radio frequencyusually refers to the range of electromagnetic oscillations with frequencies from 30 kHz to 2 GHz. In panoramic receivers, simultaneous (possibly sequential for a selected scanning time) scanning of the radio frequency spectrum is performed within several sub-ranges, usually of a decade width with a ratio of upper and lower frequencies of 10:1, in individual sub-ranges from 2:1 to 100:1. To view sections of the range near the boundaries of the sub-range, the actual scanning boundaries are 10-15% beyond the specified boundary frequencies.
Resolving powerare characterized by the smallest frequency interval between two unmodulated harmonic oscillations of the same level that can be recorded as separate. The term selectivity (or selectivity) is also sometimes used, which characterizes the ability to tune to a selected signal in the presence of interference with a close frequency. To increase the resolution of the receiver, a two- or three-fold frequency conversion is used. In this case, the ability to resolve signals with close frequencies is determined by the passband of the narrowest of the intermediate frequency amplifiers in the path. The resolution of the IFA depends on the selected subrange, in which the operator can change it by a factor of 10-100.
SensitivityThe IPP is characterized by the lowest power of the measured signal at a fixed frequency spectrum width, for example, 1 kHz, which can be received. The sensitivity limit of the IPP is determined by the level of intrinsic fluctuations of the input low-noise amplifiers. It depends on the selected bandwidth, as well as on the subrange scanning speed if the IPP is built as a sequential spectrum analyzer. Sensitivity is measured in milliwatts (mW) or in decibels relative to milliwatt (dBm).
From frequency instabilityAll the most important characteristics of the receiver depend on the reference generator of the first frequency converter: sensitivity, resolution, error in determining the parameters of the measured signal. Frequency instability for a time of less than 1 s is characterized by the spectral density of frequency noise. The ratio of the frequency noise power in a 1 Hz band to the signal power [1/Hz] is used as a measure of this value. This value is usually indicated in a logarithmic decibel scale. The relative spectral density of noise changes depending on the values of the carrier frequency itself and the small offset from it. Therefore, this parameter is often recalculated to a certain average frequency, for example, to a frequency of 1 GHz, with an also certain, for example, 10 kHz, offset from the carrier. Frequency instability over a day and a year characterizes the effects of aging and is measured in units in relation to the average frequency of the reference generator. This value is specified as the root-mean-square deviation from the nominal value in units of a certain decimal place after the decimal point or in millionths, for example, 2E-7=2X10-7=0.2 ppm.
Dynamic rangeThe IPP defines the highest ratio of the received signal level above the threshold, at which the parasitic combination components do not exceed the threshold and thus cannot be taken for a real active signal. They also introduce the characteristic of nonlinear or intermodulation distortions of the second and third order as the highest ratio of the levels of two signals concentrated in frequency, at which the corresponding nonlinear products do not exceed the detection threshold.
The types and parameters of modulation of received signals, provided in a particular IPP, characterize its ability to detect certain types of modulation (amplitude, pulse, frequency manipulation, two-level phase manipulation, etc.), evaluate some parameters of these types of modulation (deviation, pulse duration, repetition period, etc.), and in some cases, detect the information component by which modulation is performed.
Along with the above-mentioned basic parameters of the IPP, such auxiliary capabilities and characteristics of the device as the presence of memory of previous work sessions, communication with a computer for recording results and control, the ability to connect external devices and generators, the accuracy of measuring signal levels, weight and size indicators, energy consumption, price are of great importance.
Of course, the IPP intended for monitoring the electromagnetic environment near the protected object must be equipped with an antenna matched to the IPP in terms of input parameters, which has the selected properties for its directional action.
Basic level of modern IPP
Today, the Russian market is widely represented by the AR3000A, AR3000, AR5000 type IPPs by AOR Ltd., as well as the IC-R8500, IC-R9000, 1C-PC1000 type by 1COM. The mentioned devices are designed to detect the presence of uncontrolled electromagnetic radiation in the analyzed range and for a rough estimate of their average frequency, but not for precise measurements of signal parameters. They do not have internal calibration generators, the dynamic range is small. They are frequency range scanners.
Professional electromagnetic environment monitoring equipment includes some devices from manufacturers such as Rohe&Schwarz (Austria), Hewlett-Packard and TektronixAdvantest (USA). Among domestic manufacturers, the following companies can be distinguished: SKB Radio Measuring Equipment (SKB RIAL) (Nizhny Novgorod), «Elvira» (Moscow Region). Typical parameters of such IPP are given in Table 1.
A useful feature of modern devices is the ability to interface with a personal computer, portability, low weight, independent power supply.
Characteristics of some PPIs
The Tektronix 2795 is a PPI with wide functionality. It operates in the frequency range from 100 Hz to 1.8 GHz with a frequency resolution from 10 Hz to 3 MHz. This device is optimized for measurements in the meter and decimeter radio wave ranges, which are most often used for special means of information transmission. Together with the Tektronix 2795, an external tracking generator TR-503 can be used to set the average frequency of the analyzed section with the ability to reconfigure it. A set of special control tools and a user-friendly menu allow you to make all measurements using the control buttons on the front panel of the device. The Tektronix 2795 provides tools for automating complex measurements. It is possible to program the device. Data from the built-in liquid crystal display can be stored in its internal memory, as well as transmitted via the communication bus in GPIB format to other devices of the measuring complex. A frequently used sequence of measurements is recorded in the internal memory of the device and can be called up for repeated execution. The Tektronix 2795 can store up to 10 different measurement parameters in non-volatile memory. It also provides the ability to save up to 9 screen copy images, which is really convenient when data analysis can be postponed. The weight of the device without TR-503 is about 20 kg. The Tektronix 2712 model is a spectrum analyzer that has a small weight (9.5 kg) with fairly high technical characteristics. The Tektronix 2712 operates in the frequency range from 9 kHz to 1.8 GHz. In addition to the basic delivery, it can be equipped with an external or internal tracking generator, a quasi-peak detector, a serial port for digital communication in the RS-232 format. The Tektronix 2712 measuring receiver is also optimized for operation in the meter and decimeter wavelength ranges. It has the necessary set of tools for full programming of operating modes. It has a built-in non-volatile memory (124 Kwords), where up to 108 screen copy images can be stored. It is possible to control the device from a computer via a GPIB bus or via a serial interface of the RS-232 port.
The Hewlett-Packard 8591E measuring receiver is an easy-to-use portable spectrum analyzer that allows measurements in the frequency range from 9 kHz to 1.8 GHz. A unique feature of the 8591E receiver is the ability to analyze the spectrum composition using a fast Fourier transform in the low-frequency range (30-300 kHz) by pressing just one button. The device provides programming and storage of programs and data in the internal memory of up to 512K. The on-screen interface of the built-in display is similar to Windows programs. The 8591E provides the ability to interface with a personal computer for control and data output via a bus in the HP-1B standard or via a serial interface in the RS-232 format. Hewlett-Packard offers a new low-cost portable spectrum analyzer ESA-L1500A, operating in the frequency range from 9 kHz to 1.5 GHz with a small frequency measurement error (±2 kHz at 1 GHz). The device is easy to operate, has a Windows-type screen interface and is compatible with a personal computer via the HP-1B bus or the RS-232 serial interface. The device has a built-in tracking generator for setting the average frequency value of the analyzed frequency interval. Depending on the options, the weight of the device varies from 12.3 to 25 kg.
The FSA spectrum analyzer from Rohe&Schwarz is a professional laboratory (weight 50 kg) device with very high technical characteristics. Its advantages include a wide range of operating frequencies (from 100 Hz to 1.8 GHz), a large dynamic range, a low level of phase noise and parasitic frequency modulation, and an internal tracking generator. The device is fully programmable and can be interfaced with a personal computer via a serial interface in the RS-232 format. A standard computer disk drive for 3.5″ or 5″ disks can be connected to the device.
The portable spectrum analyzer U3641 from Advantest is the most compact device of its class. Its weight is 6.9 kg, the additional built-in battery weighs 2.1 kg. The device operates in the frequency range from 9 kHz to 3 GHz.
The Belan panoramic near-field receiver was developed by specialists from the domestic manufacturing company Elvira. The device has an operating frequency range from 100 kHz to 2.1 GHz. In essence, it combines the functions of a spectrum analyzer and a search complex. It has three operating modes. In the receiver mode, demodulation of amplitude-modulated (AM) or frequency-modulated (FM) signals is performed at a selected frequency. In the spectrum analysis mode, an image of the spectrum module of signals detected in the scanning band is induced on the display and periodically updated. The search mode is designed to register radio signals whose amplitude exceeds the threshold value set by the operator. The Belan device has an internal non-volatile memory, which can store up to 1000 frequency values of previously detected signals. The device is fully programmable and interfaced with a personal computer via an RS-232 serial port. It is easy to use, has a nice screen interface, low weight (6 kg) and the ability to independently power supply. Its significant advantage compared to the devices mentioned above is its 2-3 times lower cost. A certain disadvantage of the Belan receiver is the lack of a tracking generator. It would be possible to provide for the presence of «hot» buttons in the screen interface program for quickly selecting individual menu items.
The domestic IPP «Prizer-2» manufactured by SKB RIAL operates in the frequency range from 20 MHz to 1 GHz, has a sensitivity of up to -60 dBm, a resolution of up to 200 Hz, a dynamic range of up to 90 dB, a panoramic indicator, a mode for storing spectrograms and measurement results, an RS-232 interface, and a weight of 5 kg. Table 2 provides comparative technical characteristics of the IPPs currently available on the market.
The above analysis of measuring panoramic radio frequency receivers shows that the market currently has highly sensitive and at the same time compact equipment for detecting sources of electromagnetic radiation that can interfere with other radio electronic equipment or signal an unauthorized breach of office security. Such devices use high-quality components of electronic equipment and information technology, so their cost is relatively high (from units to tens of thousands of US dollars). At the same time, the importance of the security problems solved with the help of such products may well justify the costs.
Domestic manufacturers are currently introducing open IPPs to the market that are not inferior in their technical characteristics to the best foreign models. At the same time, their cost on the domestic market is 2-3 times less.