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Principles of formation of discriminatory responses of discriminators


V.V. Bessonov, S.V. Ponomarev

In the paper, a method for formation of discriminatory response (DR) of phase, frequency, correlation, and time discriminators with a prederemined law of DR variation, based on widely known modern discriminators (detectors), is described. The main attention is paid to the statement of the principle of phase discriminator operation, whose characteristics is the most different from DRs of other discriminators. For this purpose, the ordinary phase detector (PD) with sine (or cosine) response is used, whose voltage at moments defined by the clock frequency is measured and transformed by the analog-to-digital converter (ADC). This voltage forms the address in ROM, where previously the sine (or cosine) voltage code is written, which has the same amplitude as the voltage fed to ROM from PD1 (ADC). This is the most important condition in the design of such discriminators. In each ROM cell, a number is written in advance, corresponding to a predetermined law of DR variation. From ROM cells digits are sent to digital-to-analog convereter (DAC) where the step-wise voltage is then fed to the low-pass filter. Since the sine function is symmetrical in 1-2 and 3-4 quarters, then, to compensate this uncertainty, the second PD with cosine (or sine) amplitude-frequency responce is added so that the response signs of these two PDs in all four quarters of the period do not repeat. Thus the uncertainty is eliminated. The device was modeled in program Proteus. As an input signal, the part of the audio file Ave Maria.wav was chosen, which also was heard on the device output. Good results were obtained. The frequency discriminator also has two indication uncertainties of positive and negative polarities. To compensate them, two additional frequency detectors are used, whose DRs are passed through diodes which «cut off» the negative «half» at elimination of the positive uncertainty, and «cut off» the positive «half» at elimination of the negative uncertainty. Everything else in the frequency discriminator evaluation is the same as that for the phase discriminator. Since the shapes of DRs for correlation and time discriminators are similar to the shape of the frequency discriminator DR, their evaluation is analogous to evaluation of the frequency discriminator.
June 24, 2020
May 29, 2020

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