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Power amplifier for shortwave radioamateur bands
Smutný, Štěpán ; Šebesta, Jiří (referee) ; Lukeš, Zbyněk (advisor)
The amplifier is designed in the class AB, for which is typical acceptable efficiency and relatively low quiescent power consumption. As active components, the MOSFETs transistors are used. Their quadratic transfer characteristic allows for a gain control by means of quiescent current setting. The principle of MOSFETs function will be described, along with their utilization in the class AB amplifier. Since the amplifier processes signals in the shortwave band, parasitic capacitances of the transistors reduces gain greatly. Therefore, these capacitances will have to be compensated by positive feedback. First, the function of the amplifier will be verified in PSPICE program, then design or selection of real components (including transformers, heat sink and bias control) will be carried out. By performing measurement on assembled amplifier, we have verified the gain control (doubling the quiescent current increases gain by 3dB). If the quiescent current is set to 1250mA, the gain exceeds 20dB in the range from 1.4MHz to 13.5MHz. Gain at high frequencies was achieved thanks to compensation by positive feedback.
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