Three-point switching

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Three-point circuit with tube

The three-point circuit is an oscillator circuit for generating high frequency . It is an oscillating circuit undamped by feedback .

Depending on whether a coil or a capacitor is used for feedback, one is created

The resonant circuit consists of the left coil and the series connection of the two capacitors with 100 pF and 30 pF. There is a phase shift of 180 ° between the upper and lower end of the resonant circuit. This fulfills the feedback condition because the amplification circuit, an electron tube is used in the circuit shown , creates an additional phase shift of 180 ° between the control grid and anode.

The 33 kΩ resistor ensures that electrons that accidentally land on the control grid are diverted to the cathode. The coil with 100 turns allows the direct current to pass to the supply, but decouples the generated high frequency to flow away to the power supply.

If the inductance of the coil and the electrical capacitance of the capacitor are continuously reduced , the natural frequency of the resonant circuit increases . In extreme cases, the coil only consists of half a turn and the capacitor consists of the capacitance of the tube.

literature

  • Helmuth Willems, Hans Mohn, Dieter Blank: Electrical engineering Volume 3: Communication technology . 2nd Edition. Springer-Verlag, 2013, ISBN 978-3-663-01155-2 , pp. 255-257 .