Wien Bridge Oscillator

Discussion in 'Wireless & RF Design' started by nerdegutta, Oct 28, 2010.

  1. nerdegutta

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    Dec 15, 2009
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    Hi.

    I'm just wondering... The Wien Bridge frequency formula, according to Wikipedia, is:

    f=1/2∏RC

    so, if I use a 1M resistor and a 0,1F capacitor:

    f = 1 / 2 x 3,14 x 1 000 000 x 0,1 = 628 000 Hz / 1000 = 628KHz

    Is this correct?

    And am I able to use this in a RF transmitter circuit?
     
  2. t_n_k

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    Actually it's 1/(2∏RC) - so your values would give 1.59Hz.
     
  3. t_n_k

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  4. nerdegutta

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    Nice! Thanks!

    I will read...

    Is it possible to use this type of oscillator in a RF transmitter circuit. What kind of oscillators is best in RF. Wien-Bridge, Hartley or Colpitt's? The frequency is in the 500 - 1600 KHz range.

    I am kind of hoping the Wien-Bridge, because I'm struggling with the air-core coils. :(
     
  5. t_n_k

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    The Wein bridge probably wouldn't be the best choice - I've not seen in used in conventional RF circuits. However the link I gave does suggest stable operation above 1MHz is possible with the right components.

    What do you actually want to do? There may be laws in your country which limit the permissible power output from an oscillator radiating in the AM band.
     
  6. nerdegutta

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    Yes, I know. There are regulations. I'm just trying to learn about RF, oscillators and transmitters.
     
  7. bertus

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  8. nerdegutta

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    I'm currently reading:

    "RF Components and Circuits", by Joseph Carr. There he is not mentioning the Wien Bridge. I thought that this oscillator would be easier to build, without the home-made coil.

    I have succssfully built a small FM transmitter, but the frequency is a bit unstable. And my first guess is the coil. (The range is about 100m)

    That's why I'm interested in the Wien Bridge.
     
  9. bertus

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    Hello,

    Here is an example of an 1 Mhz wien bridge oscillator:
    http://www.jensign.com/wien/index.html

    The circuit build on a breadboard will give more trouble than on strip- or veroboard.

    Bertus
     
  10. skeptic

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    Mar 7, 2010
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    Why don't you look into crystal oscillators like the Pierce?
     
  11. Wendy

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    Air cores are generally not the problem, since they aren't affected by temperature. Solid state devices in general are the culprits there.

    You must have a really stable power supply voltage with lots of noise bypass (capacitors). This is a given, and much more likely to affect frequency stability. Simple three terminal voltage regulators, or even zener diodes, are your friend.

    If it is a permanent project, putting it in a metal box is always a good idea for the final layout.
     
  12. t_n_k

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  13. nerdegutta

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    Skeptic:
    This is kind of what I was hoping would show up. Thanks.

    Bill_Marsden:
    I thought it was my coils. I've read alot, and I've worked my way thru different calculators. It seemed to me that I could not get the diameter, length and number of turns right.

    Regarding the powersupply. At first I tried with a "jump-started" ATX PC powersupply. This didn't work very well. Lots of noise or something.

    Then I tried with a 9v battery. This was much better. Maybe I should use a LM7805 and some capacitors? Never thought of that. Thanks.

    t_n_t:
    Thanks for the link. I will read.
     
  14. Wendy

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    If you have stiff wire coils are easily adjustable, by the simple expedient of spreading the coils apart (very carefully, very slightly) or compressing them together. The formula's get you in the ball park, but fine tweaking is an art.
     
  15. bertus

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  16. nerdegutta

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    That is true. I usually wrap wire in the threads of a bolt. After that I carefully "un-screw" the bolt. That leaves me with a somewhat nice coil.

    Thank you for the links, Bertus. I guess you have a link for nearly everything. :)
     
  17. Wendy

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    A bolt? Hopefully you don't leave the bolt in place. The core dramatically affects frequency responses (which is why air is so popular).
     
  18. Kermit2

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    Freq drift and stability over short duration time spans(surge and sag) can be a problem in LRC component oscillators. Depending on the application, crystal control, or Digital PLL control, may be the only way to get acceptable transmit and receive frq stability.
     
  19. nerdegutta

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    Bill_Marsden:
    I remove the bolt, so I end up with an Air Core Coil...


    Kermit2:
    Where do I find information about Digital PLL? Do you have some good links or ... Ah... I know "Google it." :) I will.

    Thanks!
     
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