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  1. #1
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    Crystal Oscillator Design

    HI, i Just wanted to understand this circuit better and discuss with people

    So here it is a ,crystal oscillator...



    It uses a 3.5Mhz Crystal... and takes feedback from emitter of the transistor ,using a Capacitive Voltage divider...
    And it has 50pF Variable cap,i think it is to tune the frequency of the oscillator,am i right??

    my another doubt is there are 2 capacitors 270pF and 150pF,do u think that will add up to the frequency ???
    Please correct me ,if i am wrong and also explain it's working in brief for my better understanding

    •   Alt12th December 2011, 19:25

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  2. #2
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    Re: Crystal Oscillator Design

    "my another doubt is there are 2 capacitors 270pF and 150pF,do u think that will add up to the frequency ???" They will have a very small (+-10HZ) effect on the frequency but a huge effect on the output level and if the oscillator will oscillate at all.
    Frank



    •   Alt12th December 2011, 21:28

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    Re: Crystal Oscillator Design

    On your schematic, the Colpitts-type oscillator is shown. The capacitors between transistor base and ground are calculated for a coil in place of the quartz crystal. The L1 in collector is tuned by 250 pF variable capacitor to resonate at 3.56 MHz for a good oscillation. Fine tuning can be done with 50 pF VXO in series with the quartz.

    Find a textbook on the basics of RF electronics to learn how oscillators function, and try to make experiments. Try ARRL Radio Amateur's Handbook, you can find a lot of good stuff, and well explained.



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