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Clapp Oscillator

Discussion in 'Electronics Homework Help' started by Newb, Oct 16, 2011.

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  1. Newb


    Oct 16, 2011
    I'm having some trouble with my lab report on clapp oscillators. My theory class and lab are on separate days and my lab is moving faster than the stuff I learn in lecture. The lab instructor went over some of it but I'm still a little lost.

    My 1st question is how do you find out the efficiency of the oscillator?

    And how do you know if oscillation is sustained? I know two capacitors provide the proper feedback for oscillation and if either fails the oscillator won't work either. Do I calculate the gain? If so what gain am I supposed to get for it to be sustained?

    Thanks for the help!
  2. duke37


    Jan 9, 2011
    Efficiency is defined as power-out divided by power-in.
    Power-in is voltage-in times current-in.
    Power-out is voltage-out (RMS) squared divided by load resistance.

    The easy way of finding out if the oscillations are sustained is to look at the output with an oscilloscope or an AC voltmeter which can measure at the frequency produced.

    An oscillator is an amplifier with a gain of more than one with the output connected to the input. In the case of the Clapp oscillator, the intention will be to get a sine wave out. If the gain is more than one, the waveform will be clipped and the sine wave distorted. It is thus necessary to have some system to reduce any excess gain so that oscillation is only just maintained at the amplitude required.
  3. foTONICS


    Sep 30, 2011
    So would AGC be this 'system' your talking about?
  4. duke37


    Jan 9, 2011
    Yes, AGC is automatic gain control.
    In the days of Mr Clapp, the valve (tube) would take gid current which would bias the valve to take less current so restrict the amplitude. A similar method has been used with a diode on transistor oscillators. Variable resistors such as varistors or filament lamps have also been used to stabilise the output. Generally, the less the stabiliser has to do, the purer the sine wave.
  5. Will D

    Will D

    Mar 14, 2012
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