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Output generating circuits - generating continuous oscillations
.. Electronics

Output generating circuits

It is known that the output you get in electronic circuits is generated by oscillators or amplifiers or some other circuits as needed.

Figure (218) shows an inductive coil L and a capacitor S connected in parallel. In addition, the electromagnetic field in the coil can store energy if a certain electrical voltage arises on its inductance, and at a certain moment. This field quickly collapses, generating an electromotive force that charges the capacitor, which soon begins to discharge its charge, returning the energy it took to the inductor. It is worth noting that this process continues indefinitely, but the presence of resistors in the circuit leads to the reduction of these oscillations, which gradually fade away until they finally disappear.

The value of the oscillation depends on the values ​​of both the capacitor and the inductor, according to the following equation: D = 1 / T L S, where L is expressed in henry, S in farads, and D in hertz.

218 - Oscillation in a circuit containing an induction coil and a capacitor.

Generating sustained oscillations

The oscillations produced in the previous circuit can remain, without fading, if we add a device to the circuit that compensates for its lost energy. Figure (219) shows a circuit for generating sustained oscillations that includes a resonant circuit composed of coil L1 and capacitor S. As for coil L2, it is a coupling coil that returns energy to L. In addition, the DC generated in L1 can reach the control network of valve S, and results in an amplified signal that is generated on the elevator A. Then the coil L2 sends energy to L1 by feedback and in the same phase, thus we get continuous oscillations.

219 - Feedback helps to maintain the oscillation continuity

220 - Variable frequency oscillator
221 - Mixer circuit and oscillator circuit in a receiver already above the heterodyne

A variable capacitor SM (220) is usually used to create resonance in the circuit that includes a certain range of frequencies. As for the coil L1, it is changed over a broader range of frequencies. The rectification process between the network and the cathode helps in the appearance of a negative charge across the capacitor S and the resistance, which is sufficient to create stable operating conditions. Most valve receivers include such a circuit where the oscillator is the triode section of a triode or any "frequency-changing" valve. Figure (221) shows the following components: resistor M1, capacitor S1, variable capacitor Sm, coil L1, coil L2 with the triode. The control network adjusts the current intensity in the heptadecimal valve's anode. In addition, the coil is tuned so that the difference between the frequency of the received signal and the resonant frequency in the coil L is always constant. The mixing process in the heptadecimal valve results in a constant frequency signal appearing on the anode. The valve output then passes to the fixed tuning circuits of the intermediate frequency transformer. The capacitive tuning capacitor is useful in covering the frequency range for which coil L1 was designed.