FM coil

Discussion in 'Wireless & RF Design' started by nerdegutta, Dec 26, 2009.

  1. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi Gurus.

    I've been looking for an explanation on coils for a simple FM transmitter, and FM receiver.

    Once I bought a FM receiver kit, one of the parts, were a steel wire I was supposed to wind up to form a coil. The kit didn't work well. All I heard was "flopp-flopp-flopp" sound. So I put that away.

    On the Net, I've seen explainations (correct spelling?) on how to make good coils. See the attached files: complete turns & L3_2. This looks like copper-wire to me.

    In the attached file t7000-2, you see a coil, etched in the PCB.

    And here's my question:

    What is the best way to make a coil? Is it using a screw with the proper diameter and follow the threads with copper - wire? Or steel - wire? Or do you get the same result by etching it in the PCB?


    Jens
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In the description they talk about siver coated wire.

    [​IMG]

    As told the windings may not make contact with eachother.

    Also take care of the correct mounting of D1 (the varicap).

    I also attached the datasheet and aplication notes of the TDA7000 recieverchip.

    Greetings,
    Bertus
     
  5. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Thank you, Bertus.

    I will inspect my soldering, again.

    You have been most helpful. :)

    Jens
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    The usual way I wind small coils is to close-wind on an appropriate diameter item such as the shank of a twist drill or bit of plastic tubing.

    Form the 'legs' before taking the coil off the 'former' so as not to distort the coil.

    Remove the former and gently stretch the coil to the correct length by gripping the legs and/or end turns.

    That should give even spacing between turns over the length of the coil.
     
  7. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
    2,515
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    Hi,

    my bits holder for my drill makes exactly 10mm diameter air coils, and I've also had success with winding them in the threads of a 10mm screw. This makes perfect space between the turns.

    I have also used this link for calculating:

    http://208.94.242.202/~sm0vpo/begin/calc-00.htm

    Thanks for reply.


    Happy new year to all. Let's hope 2010 brings money and joy. :)

    Jens
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    The TDA7000 is not made anymore. It was replaced by the TDA7088 that scans for tuning.
    Both have very poor performance as an FM radio and the entire radio with a battery and earphones is sold in The Dollar Store for only $1.00.
     
  9. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi,

    I know that it is not made anymore. :( Do you know if there is a substitute or similar kind of chip?

    Jens
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I said that the newer TDA7088 replaces the old TDA7000. The TDA7088 is in the poor quality scanning FM radios sold for only $1.00. I think it is made only in a tiny surface-mount package.
     
  11. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Yes, you did. My fault. I'm sorry...
     
  12. radiohead

    Active Member

    May 28, 2009
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    Here's an interesting project for an FM receiver... use an MPF-102 FET.
    I found this "Radio Shack Special" on the web somewhere. It works, although not very well. Just google 'radio shack special' and you'll find it.
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    The Radio shack Special is a super-regenerative "radio".
    It is overloaded by strong local stations.

    It detects AM, not FM but if you tune it to one side of an FM station it "slope-detects" by changing the frequency changes into amplitude changes.

    It "squelches" which is it turns itself on and off at an ultrasonic frequency so it is very sensitive but that beats with the 19kHz and 23kHz to 53kHz of stereo FM which causes whistles.
     
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