A hardware prototype of the two-stage Colpitts oscillator employing the microwave BFG520 type transistors with the threshold frequency of 9 GHz and designed to operate in the ultrahigh frequency range (300-1000 MHz) is described. The practical circuit in addition to the intrinsic two-stage oscillator contains an emitter follower acting as a buffer and minimizing the influence of the load. The circuit is investigated both numerically and experimentally. Typical phase portraits, Lyapunov exponents, Lyapunov dimension and broadband continuous power spectra are presented. The main advantage of the two-stage chaotic Colpitts oscillator against its classical single-stage version is in the fact that operating in a chaotic mode it exhibits higher fundamental frequencies and smoother power spectra.
We describe an extremely simple second order analogue electrical circuit for simulating the two-well Duffing-Holmes mathematical oscillator. Numerical results and analogue electrical simulations are illustrated with the snapshots of chaotic waveforms, with the phase portraits (the Lissajous figures) and with the stroboscopic maps (the Poincar´e sections).
PSpice simulation and experimental results demonstrating chaotic performance of the Colpitts oscillator in the ultrahigh frequency (300-1000 MHz) range are presented. Various combinations of the resonance tank parameters are considered to achieve a fundamental frequency as high as possible. Simulations indicate that chaotic oscillations observed experimentally at higher frequencies, e.g., at about 1000 MHz are caused by parasites, like wiring inductances, loss resistance appearing due to skin effect, and collector-emitter capacitance of the transistor. Reliable and reproducible chaos can be generated at fundamental frequencies up to about 500 MHz with the single-stage Colpitts oscillator using the microwave 9 GHz bipolar junction transistors.
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