Clapp oscillator

The Clapp oscillator was developed by James K. Clapp and 1948 published. According to an article by Vačkář the principle of other engineers developed independently; a variant of Gouriet had been since 1938 on the BBC in operation. It can be regarded as an improvement of the Colpitts circuit.

Amplifier as an electron tube has been used (Fig. 1). The frequency-determining resonant circuit composed of the coil and the three series-connected capacitors. Here, the frequency-determining capacitor C1 is not included in the positive feedback. The other two capacitors C2 and C3 form a voltage divider, to which a part of the resonance circuit voltage is fed back to the cathode, thus strengthening as in the Colpitts circuit.

The circuit is suitable for high frequencies, where high frequency stability is required and a coil tapping as in Hartley oscillator is not practical.

Below ( Figure 2 ) is a basic transistor circuit in the form of the emitter follower or common collector circuit that does a considerably lower voltage. Compared to the previously invented Meissner oscillator or Hartley oscillator these circuits require only one coil without tap. The resonant circuit capacitor C is divided into the three capacitors C1, C2 and C3. The high frequency alternating voltage on the upper terminal of C2 is twice the size of the upper port of C3. The voltage gain of the transistor 0.99 and the voltage divider R3, R4 to a total voltage gain of about 1 as for an oscillator provides necessary. Resistors R1 and R2 determine the operating point of the transistor. About C4, the output of the oscillator is extracted.

Tuning oscillator for a superheterodyne receiver in the Clapp oscillator for higher frequencies is better suited as the Colpitts oscillator. The tuning capacitor C1 is connected to a terminal to ground. Furthermore, the overall gain between low and high frequency oscillator oscillator frequency does not change as much as the Colpitts oscillator. Hartley circuit is also suitable for the local oscillator, when a coil tapping is acceptable.

The data of coil and capacitor of the resonant circuit essentially define the frequency generated by the Thomson's resonance formula. The additional capacity of the remaining components reduce this calculated frequency.