RF Varactor Recommendation: QUICK HELP PLEASE

Discussion in 'General Electronics Chat' started by Management, Jun 23, 2008.

  1. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Does anyone know of any good Varactors that are used in RF circuits?

    I need low noise, high Q, with a high a C span as possible. I'm not limited to the amount of reverse bias voltage need to change the capacitance.

    A few recommendations would be GREATLY appreciated. I check Digi-key and Mouser but don't know which ones fall into my category. Can someone help me out or if they know any off hand that would be great too. I need to order some.

    Thanks in advance.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    What frequency range are you dealing with?
    What is the range of capacitance you're looking for?

    You DO know that you can run several of them in parallel to increase total capacitance and range, right?
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    To further SgtWookie's comment - the varactor works in concert with an inductance to form a resonant circuit. Therefore, the value of the inductor has a lot to do with the choice of capacitance. There is also the intermediate frequency to be considered, if the radio is the superheterodyne type.

    We need more information to be able to suggest a device.
     
  4. Management

    Thread Starter Active Member

    Sep 18, 2007
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    I want to resonant a LC tank circuit at 64 MHz. The inductor will most likely be 51 nF so that leaves the cap at about 120 pF.

    From what I got on Digikey I figured I would have had to put some caps in parallel.

    Just don't know which would be best to give me the highest Q. I guess that is priority over what the C range is and also low noise. Those are the two most important factors for me.

    Thank you for the responses.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Caps generally have VERY high Q in comparison to inductors. It's the Q of the inductors that is the real challenge.
     
  6. Management

    Thread Starter Active Member

    Sep 18, 2007
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    So what do you think would work from Digikey? I want a few suggestions. I can order more than on type/manufacturer/part.
     
  7. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Also, can someone help me figure out ho to test how noisy a Varactor would be? How would I be able to determine a qualitative value for noise. Characterizing it basically.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    The manufacturer's data sheet should have an expected value on it, and perhaps include the test rig.
     
  9. Management

    Thread Starter Active Member

    Sep 18, 2007
    306
    0
    Anyone know an good varactor models? Or where I can get some.
     
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