Abstract
The object of research is the process of interference suppression in a passive radiometric receiver, centered over the interference spectrum, with a random or varying frequency. Noise immunity can be increased by means of special circuits preventing the receiver from overloading and using differences in the characteristics of useful signals and interference to suppress the latter. As a rule, the frequency of noise oscillation is never accurately known and, in addition, the actual interference is never purely harmonic. Therefore, it became necessary to theoretically consider the degree of interference suppression by the input circuit of the radiometer at an unknown value of the interference frequency and the finite width of the spectrum, and also theoretically substantiate possible ways of constructing adaptive devices for suppressing real narrow-band noise. An expression is obtained for the suppression coefficient of the interference concentrated on a spectrum, which shows that the interference will be suppressed automatically for the optimal choice of the parameters k a , τ, T of the servo system. In the paper, a functional diagram of a radiometric receiver is presented, which uses an adaptive system to suppress the spectrum-centered interference. The adaptive system is based on the inclusion in the radiometric receiver circuit of additional compensating circuit interference. The interference compensating circuit makes it possible to increase the sensitivity of the receiver to 10 -20 W with an accuracy of 0.1 oC and a response rate of 2...4 s. In addition to interference suppression, the compensating link after the intermediate frequency amplifier is provided with interference suppression and an input circuit. In this case, the overall amplification in the noise immunity of the radiometric receiver in comparison with the compensating receiver, as calculations for typical characteristics show, will not be worse than 30 dB.
Highlights
Systematic control over the health of farm animals becomes a necessary condition for the functioning of livestock complexes, and its improvement is one of the most important tasks of veterinary science and best practice [1]
The analysis of existing radiometric receivers shows that their parameters do not meet the requirements for accuracy, sensitivity and noise immunity
The aim of research is a theoretical analysis of the ditionally includes an interference compensating circuit, circuits in the structure of a radiometric receiver for which is installed in the intermediate frequency amplisuppressing a noise concentrated on the spectrum, with fier (IFA) channel after the frequency conversion, as well a random or varying frequency
Summary
Systematic control over the health of farm animals becomes a necessary condition for the functioning of livestock complexes, and its improvement is one of the most important tasks of veterinary science and best practice [1]. In veterinary practice contact (thermometers) and non-contact (thermal imagers) methods of temperature measurement are used. Preference should be given to a remote method based on the reception of the thermal radiation of the animal organs. The analysis of existing radiometric receivers shows that their parameters do not meet the requirements for accuracy, sensitivity and noise immunity. A millimeter-wave radiometric system for measuring the animals’ own electromagnetic radiation, having a relatively wide reception band, can be exposed to a combination of interference [3]. A practical analysis shows that one of the dangerous is a spectrum-focused interference with a random or varying frequency, which can be suppressed by means of special circuits using differences in the cha racteristics of useful signals and interference [5]. Suppression of a noise-centered noise, with a random or varying frequency, is an actual problem
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