Voltage tuned xtal oscillator problems

Discussion in 'Wireless & RF Design' started by hafrse, Jun 27, 2013.

  1. hafrse

    Thread Starter New Member

    Jun 27, 2013
    3
    0
    Hello,

    I have problems with a voltage tuned 29Mhz xtal oscillator, it has no output signal. Checked the bias of the transitor, all ok, replaced thre transitor, varicap and the x-tal, still the problem exist.
    It can be a component that went out of spec. I do not have schemtics but tried to drow the wiring of the oscillator and it is attached. also, desoldered all the caps and took there value by a capacience meter, but values below 20pf can not be measured.


    My first question, does this circuit represent a complete 29Mhz Oscillator ? the reason I am asking is that I could have missed other components on the curcuit board beloging to the oscillator. L1 is 560nH.

    Description of the circuit:

    Input power is 10V
    Bias input isalways -5.2.
    Tune voltage is 3.72V when the instrument is powered on.
    Any hints what I can do or test?

    Thanks
    George
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    You can't voltage tune a xtal oscillator. That is what the xtal is for.
    Unless you are referring to trimming to 10ppm.
     
  3. hafrse

    Thread Starter New Member

    Jun 27, 2013
    3
    0

    Corrected circuit uploaded
     
  4. hafrse

    Thread Starter New Member

    Jun 27, 2013
    3
    0

    Correct, it is only for fine tuning to be mixed with an IF signal.

    Thnaks
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    With a varactor diode, you can only do a minuscule amount of tuning. However..for troubleshooting purposes, bypass the varactor and see if it oscillates.
     
Loading...