3-18pf air core capacitor

Discussion in 'Wireless & RF Design' started by AnonymousNerd, Apr 14, 2010.

  1. AnonymousNerd

    Thread Starter New Member

    Mar 5, 2010
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    Hi,
    I am building this little FM transmitter:http://aaroncake.net/circuits/fmtrans.asp. It calls for a 3-18pf air core variable capacitor. I have many air core caps from FM receivers, but I do not know if they are the right value.
    Does anyone know of a device that would have a suitable cap in it? Does anyone know where I could see a photo of a capacitor of that size for reference?
    Thanks,
    AnonymousNerd



    P.S.
    I attached some photos of a couple that I have.
     
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    Last edited: Apr 14, 2010
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    AnonymousNerd likes this.
  3. AnonymousNerd

    Thread Starter New Member

    Mar 5, 2010
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    Thanks for the response.
    Today I found a smaller one that looks more like the one used on the transmitter. I attached a pic of it. Do you think it would work?
    Thanks:)
     
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  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    That would work also, but the foils between the plates will tear when you tune it to rough.

    The ones rjenkins showed you are more rigid and can stand more power.

    Bertus
     
  5. radrajith

    New Member

    Oct 2, 2010
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    did the fm transmitter work with ur 3-18 pf because i am using the same website too. thanks for u r photos
     
  6. AnonymousNerd

    Thread Starter New Member

    Mar 5, 2010
    6
    0
    radrajith;
    Yes it works, I used the smaller one and etched a PCB based on aaron's layout. It would probably work in perf-board if you used a similar layout but I am not total sure. As far as I know, it is best to make RF circuits as compact as possible.
    Good luck:).
    AN
     
  7. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    Remember, those things need to be tuned with a plastic screwdriver with a long bit and almost anything near them will effect their value.
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    Like sceadwian said; you need to turn the capacitors with a plastic or ceramic screwdriver.
    There are special "tuning" screwdrivers for sale.
    Most of them have two ends, one of full plastic and the other side enforced with a tiny piece of copper.

    Bertus
     
  9. radrajith

    New Member

    Oct 2, 2010
    6
    0
    i dont have the smaller tuner but i have the tuner which u showed on first message so did it work and also for the coil what did u use
     
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