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LC Oscillator

Discussion in 'General Electronics Discussion' started by Revala, Jun 17, 2015.

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  1. Revala


    Jun 17, 2015

    I'm planning on building a basic sine wave oscillator with a variable frequency range of 1 MHz to 1.5GHZ without using any microchips, timers or op-amps. Basically I'm aiming for the simplest LC oscillator circuit possible, but haven't had much sucess in creating such a circuit. Would appreciate any advice, schematics or good websites.

    Thank you
  2. ramussons


    Jun 10, 2014

    For a Frequency range 1 MHz to 1500 MHz, do you realise that the variation of LC will be (1500)^2 = 2,250,000 ? :eek:

    If you can make an Inductor Capacitor Combination that can smoothly vary over such a Large Range AND keeping in mind the Size, Weight, Magnetic and Electrostatic Flux Leakages, ....... yes, you can.

    Normally, for such Ranges, the Coverage is done in steps, say 1 MHz to 10 MHz, 10 to 100, and so on.

    Or by "Hetrodyning", where you have, say a 10 GHz oscillator and a 10 to 11.5 GHz oscillator "beating" to give a sum (20 to 21.5) and difference 0 to 1.5 which is what you need.

    making GHz oscillators is well outside my range ...:(
  3. Ratch


    Mar 10, 2013
    An oscillator needs an energy source to supply any load you attach to it and make up for circuit losses. If you are rejecting all the active elements you named above, what are you planning to use in their place?

  4. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    Such a range is beyond the capability of a beginner.
  5. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    "a variable frequency range of 1 MHz to 1.5GHZ without using any microchips, timers or op-amps" is beyond the capability of most experienced professionals if an LC network must be used to tune it. Such a wide range is usually the province of a direct digital synthesized oscillator.
  6. Martaine2005


    May 12, 2015
    I am still very impressed, I couldn't even work that out WITH a calculator.
  7. Revala


    Jun 17, 2015
    Thank you for answering my question. I might have asked the wrong question, because the problem I have, is not with the range of the oscillator. In order to have such range you would need a ridiculously large capacitor or inductor. This kind of oscillator, however is not my goal. My aim is to create the simplest lc sine wave oscillator circuit possible, that would create a stable oscillation in the frequency range of 1 MHz to 1.5 GHz. This would not be the actual range of the oscillator itself, but the circuit would be able to create a stable sine wave in this given range. The specific coverage would be of course smaller and determined by the size of the capacitor in use.
    I have tried many different circuits from textbooks and the internet. But those, for some reason, do not seem to oscillate when I recreate them in LTSpice IV or some other electronic simulator.
    To put things simple and short. I am looking for advice on creating a simple one transistor LC oscillator, that is able to create a stable sine wave in high frequencies.

    Thank you

    P.S To answer your question Ranch. I am planning on using a simple Bipolar junction transistor as the active element. There are other active elements available such as spark caps and vacuum tubes, but these operate in a much lower frequency than I want to.
  8. LvW


    Apr 12, 2014
    So you have tried different concepts which didn`t work satisfactorily (for "some reason") - and you ask us for alternatives.
    Obviously, it is not easy to answer without knowing what you have done already.
  9. BobK


    Jan 5, 2010
    Here is a Colpitts oscillator that works in LTSPICE.


    I can only get it up to a few 10s of MHz by tweaking. To get the 1.5GHz would require a specialty transistor and circuit.

    hevans1944 likes this.
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