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Need help with basic Oscillator design

Discussion in 'Electronic Basics' started by [email protected], Nov 24, 2008.

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  1. Guest

    I have some electronics theory questions and some electronics
    simulator questions pertaining to an Armstrong oscillator. I have
    done some reading and have tried to come up with a design on my own.
    Most books just show a general diagram with no specific values. I am
    trying to simulate my design in LTSpice:

    https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Armstrong1.asc

    Plotting voltages at points A and B, the circuit will work for up to
    13 seconds (.tran 13) but does something strange after 14 seconds? I
    speculate that L2 is going to keep adding more and more energy to the
    tank circuit until things get out of control. I don’t think that this
    has happened quite yet though?

    What do I need to add to the circuit to build the voltage at point A
    to a maximum altitude and keep it there?

    Any help would be greatly appreciated. Thanks
     
  2. Andrew Holme

    Andrew Holme Guest

    Right-click the .tran directive and tick the check box "start external
    DC supply voltages at 0V"

    The changes the directive to ".tran 13 startup"

    This is often necessary for oscillator simulations to run properly.
     
  3. Guest

    Thanks
    That seems to help with the simulator part. I still have the same
    theory questions along with some new ones.

    The output of the amplifier (node B) is 180 degrees out of phase with
    the input of the amplifier (node B) . It seems to me that the
    connection to the tickler coil should be reversed but when I do this
    in the simulator it does not seem to help.

    I believe that the voltage gain of the amplifier comparing node A to
    node B is around 240 which mease that the voltage at node A can't
    exceed more than about 25 mv before the amplifier starts clipping. Is
    this correct? How do keep the tank circuit under 25mv or is it
    desirable to have the clipping in the circuit?

    I also think that my turns ratio L2:L1 is all messed up but I don't
    know what it should be either. After some thought, it would seem to
    me that the overall gain (transistor amp + tickler) should be slightly
    more than 1 to handle any losses in the tank circuit. Is this true?

    I would like to know what values would make the circuit oscillate at
    159Hz and why they are the correct values.
    Can anyone help? Thanks
     
  4. Guest

    Thanks

    I just pulled the 159Hz out of thin air. I wanted to do some
    experimenting with various types of oscillators. I have seen two
    different configurations of Armstrong oscillators. One type seems to
    have the tickler coil as the input to the amplifier and the other
    seems to have the tank circuit as the input to the amplifier. My
    design is using the tank circuit as the input to the amplifier, and
    the amplifier feeds the tickler coil.
     
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