The improvement of digital communication lines of radio information transmission systems in the direction of increasing the complexity of the signal-code structures used, increasing the speed of information exchange, the use of modern channel compaction technologies, on the one hand, and the high complexity of the surrounding electromagnetic environment, on the other hand, objectively determines the need to improve the radio receiving systems of digital communication lines in the direction of increasing their noise immunity. In this regard, in order to justify the technical requirements for noise immunity to radio receiving systems of the designed transmission lines, it is advisable to take into account the basic indicators of the quality of functioning of the radio receiving device, in order to obtain analytical expressions and graphical dependencies for evaluating the noise immunity of receiving signals with more complex combined types of modulation (QAM-64 and higher), used and planned for use. Of the large number of indicators that characterize the dynamic range, the most informative and sufficiently characterize the quality of the linear path are: the dynamic range for reducing the transmission coefficient (compression) by 1 dB and the dynamic range for third-order intermodulation distortion. The effect of interference received on the side channels (which include combination and mirror), as well as on neighboring channels, limits the lower limit of the dynamic range of the receiving device and, as a result, reduces the resulting signal-to-noise ratio at the output. The degree of suppression of the combination channels is determined, first of all, by the frequency plan and the linearity of the amplitude characteristic of the mixer of the first frequency converter, the mirror channel – the quality of filtering the mirror frequencies in the input preselector, the neighboring channel – the selectivity of the filters of the main selection. In this article, an analytical model and the resulting graphical dependencies are developed to assess the degree of influence of compression distortions on the noise immunity of receiving multi-position quadrature-amplitude modulated signals, and the requirements for the value of the dynamic range of radio receiving systems are theoretically justified.

Peripheral sensors for measuring aircraft parameters are an integral part of any system for diagnostics and forecasting of technical condition. Their principle of operation in relation to operation at aviation complexes is to convert mechanical, electromagnetic or light quantities into electrical ones for their subsequent processing. The process of radiation of disturbances propagating in the material caused by the dynamic local rearrangement of the structure of materials under the action of internal stresses leading to a change in the crystal lattice or the movement of micro- and / or macrodefects is called acoustic emission. So, the analysis of differences in the form of acoustic waves allows the classification of the type of deformation: crack or plastic deformation, which allows you to more accurately determine the current state of the airframe or diagnosed nodes. The principle of operation of such sensors is based on the effect of converting the linear dimensions of a Bragg cell, made on an optical fiber, into a change in the reflected wavelength. A necessary condition for obtaining correct results of measurements of stress states is the need for temperature compensation of the Bragg cells, which is achieved by introducing additional cells that are mechanically decoupled from the material being diagnosed and react only to the temperature component. The advantage of this method is the absence of the need for additional adjustment of the cells and their alignment, as well as the independence of measurements from the effects of electromagnetic radiation; the sensors are lightweight, vibration-resistant, and insensitive to electromagnetic fields. The article presents the practical results of using fiber-optic acoustic emission sensors for diagnosing the technical condition of critical components and assemblies of aircraft, as well as outlines the prospects for their deepest integration into a unified information and analytical system for diagnosing and predicting the technical state of aviation complexes. The developed technical solutions aimed at simplifying the methods of processing broadband acoustic emission signals, which make it possible to design acoustic emission sensors based on optical fiber, are structurally simpler and cheaper, with an increased signal-to-noise ratio, due to one conversion of an acoustic-optical signal into an electrical one.

Modern trends in the development of digital communication lines of fixed information transmission services, as well as the characteristics of continuous channels today determine the noise immunity of radio receiving systems. The main directions of its increase in terms of the radio receiving device as a whole and the demodulator device in particular are as follows: reducing the frequency and nonlinear distortions of the signal in the linear path, increasing the stability and purity of the spectral line of oscillations of local oscillators, increasing the selectivity for the mirror and combination channels of reception, compensation for intersymbol and cross – polarization interference, improving the functioning of the automatic gain control device (reducing static and dynamic errors), improving the quality of the functioning of the carrier wave recovery device and the clock synchronization device. Taking into account all of the above factors in order to increase the overall noise immunity of a digital communication line is a very difficult and urgent task, the solution of which must begin with the development of a mathematical model of a continuous digital communication line channel. This article discusses the radio receiving path of a digital communication line in an urban environment. The obtained analytical expressions are aimed at interpreting the processes of converting digital signals in the structural elements of radio receiving systems. The originality of the mathematical model developed in the article lies in the fact that it additionally, in comparison with similar models, takes into account the following number of factors: frequency instability and phase fluctuations of oscillations of the local oscillator synthesizer, dynamic and static errors in the operation of automatic gain control devices, carrier vibration recovery devices and devices clock synchronization of radio receiving systems of digital signals.

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