Belan is the first Russian portable spectrum analyzer.
The BELAN device is designed to study the spectral characteristics of radio signals and analyze the load on radio ranges.
The device has 3 main operating modes:
SPECTRUM — operation in the spectrum analyzer mode. It is used to study the spectral characteristics of radio frequency signals.
TUNER — operation in the panoramic receiver mode. Demodulates AM and FM radio signals. Used to listen to modulating signals through headphones.
SEARCHER— operation in the search device mode. It is used to detect the operating frequencies of unauthorized data retrieval devices (radio bugs).
The device has the following technical specifications:
1. Operating frequency range 0.1 — 2200 MHz;
2. Accuracy of setting the central frequency for analysis ±10 Hz throughout the entire operating range;
3. Frequency resolution during signal spectrum analysis 1 kHz. The number of samples displayed on the spectrum analyzer screen is 255;
4. IF filter passbands at 3 dB level: 1 kHz, 3 kHz, 10 kHz, 30 kHz, 100 kHz, 300 kHz, 1 MHz;
5. Shape factor at minus 60 dB and minus 3 dB levels < 5:1;
6. Sensitivity (at 200 MHz, 0 dB RF attenuator)
< -110 dBm at 10 kHz RBW;
< -90 dBm at 300 kHz RBW;
7. Spurious FM at spans less than 1 MHz in 1 kHz bandwidth less than 100 Hz;
8. Maximum input level (RF attenuator 30 dB) 0 dBm;
9. The relative level of interference caused by intermodulation distortion at the preselector input when exposed to two signals of equal amplitude with a level of 0.1 μW and a detuning value between them of 2 MHz is no more than minus 60 dB in the operating frequency range;
10. The relative level of interference caused by intermodulation distortion at the preselector input when exposed to two signals of equal amplitude with a level of 0.1 μW and a detuning value between them of 100 MHz is no more than minus 60 dB in the operating frequency range;
11. The level of interference on mirror reception channels is no more than minus 60 dB;
12. The instability of the device heterodyne frequency (total) for 30 minutes after the operating mode setup time under normal conditions does not exceed ± 10 Hz;
13. The reference frequency source is 10 MHz
- temperature drift (0° C-50° C) ± 2.0х10-8;
- aging without correction for a year ± 5х10-8, for 10 years ± 2х10-7;
- initial setup accuracy ± 5х10-9;
14. Built-in demodulators of AM and FM signals;
15. Unevenness of the amplitude-frequency characteristic of the device in the operating frequency band is not more than ± 3 dB;
16. The wave impedance of the device is 50 Ohm in the operating frequency range with VSWR not worse than 2;
17. Input attenuator 0 — 30 dB with a step of 10 dB, the installation accuracy in the operating frequency range is not worse than ± 2 dB;
18. IF attenuator 30 dB with an installation step of 10 dB. Installation accuracy ± 0.5 dB;
19. Device screen — 14 cm, LCD type. Resolution 320×240 pixels;
20. Power supply — 220V network, external DC source with voltage of 13.8V, internal 12V battery in buffer mode. Operating time from internal battery is not less than 1.5 hours;
21. Possibility of control via computer (RS-232 port);
22. Dynamic range 110dB;
23. Accuracy of signal amplitude measurement ± 3 dB;
24. Weight with built-in battery 12V x 4Ah — 9.5kg.
The device consists of the following functional blocks:
Power supply unit (PSU) – produces supply voltages, is equipped with a built-in battery charging circuit and automatic battery connection in case of 220 V power failure.
The high-frequency unit (HF) converts the input frequency to an IF frequency of 10.7 MHz, attenuates the input signal to the required level using an attenuator.
The intermediate frequency (IF) processing unit filters the signal using an IF filter and a video filter, amplifies the signal to the required level using an IF amplifier and converts the signal using a logarithmic amplifier.
The sound control unit (SCU) demodulates the signal filtered in the IF unit using the required demodulator, and also converts the IF signal into digital form using an amplifier-limiter for precise frequency signal counting.
The digital unit (DU) issues control signals to the HF, IF and SCU units, receives commands from the SCU and control commands from an external computer, digitizes the signal from the output of the logarithmic amplifier and forms an image on the display.
The keyboard unit (BU) polls the instrument keyboard and the smooth tuning knob and transmits the codes of the pressed buttons to the CB.
The structural diagram of the spectrum analyzer is shown in Fig. 1. The signal arriving at the input of the device passes through the input filter, attenuator and gets to the mixer of the first heterodyne. The first heterodyne is built on YIG using a digital frequency synthesis circuit, the output frequency of this heterodyne is controlled by the digital block and can be changed in the range of 2.2-4.9 GHz with a step of 10 Hz. After the mixer, the signal passes through the 2.449 GHz filter and gets to the mixer of the second heterodyne, tuned to a frequency of 2.56 GHz. After this mixer, the signal passes through the 110.7 MHz filter and gets to the mixer of the third heterodyne, tuned to a frequency of 100 MHz, and from the output of this mixer, the signal at a frequency of 10.7 MHz gets to the input of the IF amplifier, and after the amplifier — to the IF filter block.The IF filter block contains a set of 7 bandpass filters for a frequency of 10.7 MHz with a bandwidth of 1, 3, 10, 30, 100, 300 and 1000 kHz. The digital block switches the IF signal to one of these filters. After filtering, the IF signal goes to the logarithmic amplifier and the demodulation block. From the demodulation block, the signal passes through the LF amplifier and goes to the built-in speaker, and from the logarithmic amplifier, the signal passes through the video filter block and goes to the ADC input of the digital block. The video filter block contains a set of 4 lowpass filters with a cutoff frequency of 10 Hz, 100 Hz, 10 kHz and 1 MHz.
A digital counter is used to accurately determine the frequency. The input of this counter receives the IF signal, amplified to a logical level and passed through a limiter. When accurately determining the signal frequency, the device finds the signal with the maximum amplitude, tunes the high-frequency block to its frequency, and measures the IF signal frequency using a digital counter. The difference between the frequency measured by the counter and the value of 10.7 MHz is a correction that must be added to the value of the HF block tuning frequency to obtain the exact value of the received signal frequency. This method of determining the frequency allows you to measure the frequency with an accuracy of up to 10 Hz.
Fig. 1. Structural diagram of the spectrum analyzer
To obtain a “live picture” on the device screen, a high tuning speed of the first heterodyne is required. A gyromagnetic resonator based on an iron-yttrium garnet YIG is used as a frequency source. The circuitry used in the device allows tuning at a speed of 10,000 frequencies per second. It should be noted that such a speed is realized when tuning the frequency in the direction of increasing its value (from a lower frequency value to a higher one) and provided that neighboring frequency values are separated from each other by no more than 70 MHz. When tuning the frequency with a step exceeding 70 MHz, the tuning speed is reduced by about half due to the need to apply control to the main YIG coil in the control circuit of which, in order to reduce the intrinsic noise of the heterodyne, fairly large capacitors are included.
The spectrogram update time on the device display depends on the spectrum width displayed on the screen and the width of the IF filter and video filter used. Obviously, the lower the video filter cutoff frequency, the more time is required to filter the signal. For all video filters used, the required delay time from tuning to the required frequency until the signal amplitude measurement is performed is calculated in advance, and this delay is performed automatically during the spectrum drawing process. The dependence of the update time on the spectrum width and IF filter is less obvious. It is clear that 250 points are displayed on the screen, for drawing which it is necessary to perform 250 frequency tunings and 250 amplitude measurements. The horizontal distance between adjacent spectrogram points is equal to the width of the spectrum displayed on the display divided by the number of points displayed on the screen. If the IF filter used covers the adjacent points on the screen, then 250 reconfigurations and measurements are indeed performed, but if the adjacent points on the screen are spaced apart by a value greater than the IF filter width, then the measurements are performed with a step equal to the filter width, and the maximum amplitude closest to this point is taken as the amplitude of the screen point. For example, to display a spectrum 2.5 MHz wide with a 10 kHz IF filter, it is necessary to perform ((2500 kHz/250 points)/10 kHz) x 250 points = 2500 frequency reconfigurations and amplitude measurements. This approach allows displaying a spectrum of any width on the display: from 0 Hz (in fact, the oscilloscope mode) to the width of the entire frequency range of the device. Moreover, the spectrum sweep time is optimal in terms of accuracy and image update rate. Photos 1 and 2 show examples of displaying the spectra of various signals. Photo 1 shows a signal with FM modulation, photo 2 shows a signal from a bug with masking using SPREAD SPECTRUM technology.
Photo 1. Signal spectrum with FM modulation
Photo 2. Signal of an eavesdropping device with masking using SPREAD SPECTRUM technology
In the search device mode, an algorithm is implemented for detecting operating frequencies of radio signals whose amplitudes exceed the threshold level set by the operator and are not included in the list of legal radio signals. The scanning process of a given range can be performed several times (from one to 255) or looped so that it is performed continuously. The viewing range can be divided into several (up to eight) subranges, each of which can have its own threshold level and attenuation levels of the input signal and amplification of the signal at the intermediate frequency. The scanning process can be interrupted either by the operator entering a new command, or terminated automatically upon completion of the required number of scanning cycles, or automatically interrupted upon detection of an unregistered radio signal during the scanning process. During the scanning process, the frequency of the radio signal is determined with an accuracy of 10 kHz. The scanning time depends on the range load with signals and the detection threshold level set by the operator. In Moscow conditions, with a threshold level sufficient to detect a radio bug with a power of 30 μW installed indoors at a distance of 50 m from the device, scanning the 5 MHz-2.2 GHz range takes no more than 15 seconds.
A few words about the strategy of storing and processing frequencies in the search mode. The working frequencies of radio signals are stored as a pair: the initial and final frequency. The initial frequency may coincide with the final frequency, but never exceeds it. The device's memory has 3500 cells for storing working frequencies (each cell stores one pair: the beginning and the end). In these cells, you can store any number of frequencies or frequency ranges of legal radio signals that should be ignored during the search. The device will store the frequencies detected during the search in the remaining free cells. Thus, the device maintains two lists. One list contains frequencies or frequency ranges that should be ignored when searching for radio bugs (hereinafter we will call it the list of rejected frequencies), and the other list contains a list of frequencies detected during the search, organized as a list of frequencies or frequency ranges. In the first case, the initial and final frequencies coincide (hereinafter we will call it the list of detected frequencies). Any frequency can be present in only one of these lists. For example, if the frequency 105.7-105.7 was in the list of detected frequencies, then after entering the range 105.0-106 into the list of rejected frequencies, the frequency 105.7-105.7 will be automatically deleted from the list of detected frequencies.
Frequency lists are stored in the so-called FLASH memory of the device and do not disappear after power is turned off. It should be noted that in the TUNER or SPECTRUN mode, you can press one button to re-tune to the detected frequencies in ascending or descending order of their magnitude, which facilitates the analysis of the scanning results.
The device has commands that allow you to easily compare the radio range load when searching for radio bugs. For example, you can perform several scan cycles in a room that is known to be free of bugs, but has similar radio signal reception conditions to the room being investigated (height above ground, wall material, room dimensions of windows and doorways, window orientation to the cardinal points, height and location of neighboring buildings). Then, by pressing one button, you can transfer the descriptions of all detected legal radio signals to the list of rejected frequencies. After that, the device can be turned on for scanning in the room being investigated. Most legal stations will be rejected, and this will dramatically reduce the number of signals that need to be checked for bugs.
Recently, the amplitude-difference method of detecting radio bugs (by the difference in signal amplitudes on the reference antenna and the antenna inside the room) has become very popular. At the customer's request, the device can be equipped with an antenna switch controlled by a computer and software implementing the amplitude-difference method of detecting radio bugs. The program runs in the WINDOWS OS and, in addition to detecting radio bugs using the amplitude-difference method, also records the time of the radio bug signal appearance, turns on an audible signal when a radio bug is detected, prints out the spectra, and keeps a protocol of radio broadcast observations.
The spectrum analyzer is currently undergoing certification in Rostest as a measuring device. In June 2000, it is planned to include the device in the state register.