This paper describes, based on both numerical and experimental bases, the evolution of chaotic and, in some cases, hyperchaotic attractors within mathematical models of two two-port analog functional blocks commonly used inside radio-frequency systems. The first investigated electronic circuit is known as the cascoded class C amplifier and the second network represents a resonant amplifier with Darlington’s active part. For the analysis of each mentioned block, fundamental configurations that contain coupled generalized bipolar transistors are considered; without driving force or interactions with other lumped circuits. The existence of the structurally stable strange attractors is proved via the high-resolution composition plots of the Lyapunov exponents, numerical sensitivity analysis and captured oscilloscope screenshots.

This paper describes a design process for a universal development kit based on an analog computer concept that can model the dynamics of an arbitrarily complex dynamical system up to the fourth order. The constructed development kit contains digital blocks and associated analog-to-digital and digital-to-analog converters (ADCs and DAC), such that multiple-segmented piecewise-linear input–output characteristics can be used for the synthesis of the prescribed mathematical model. Polynomial input–output curves can be implemented easily by four-quadrant analog multipliers. The proposed kit was verified through several experimental scenarios, starting with simple sinusoidal oscillators and ending with generators of continuous-time robust chaotic attractors. The description of each individual part of the development kit is accompanied by links to technical documentation, allowing skilled readers in the construction of electronic systems to replicate the proposed functional example. For this purpose, the electrical scheme of the hybrid analog computer and all important source codes are available online.

This article deals with design and experimental verification of a single stage transistor amplifier in class C which is introduced to chaotic state. The basic procedure of deriving differential equations and representation of dynamical system is presented. Equivalent circuit of transistor stage was transformed to the real model based on operation amplifier integrators. Chaotic behavior was confirmed by strange attractors captured by oscilloscope.

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In this article, a new approach for hiding personal information in speech is proposed. Speech modification is based on the long-term voice spectrum that reflects the individuality of the vocal tract. The depersonalized speech signal was objectively evaluated using fundamental frequency and intelligibility. The advantages of the proposed approach compared to the traditional technique based on normalization of vocal tract length are briefly discussed.