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Wireless Mic Schematic - help please

Discussion in 'Radio and Communications' started by DDasha, Mar 13, 2011.

  1. DDasha

    DDasha New Member

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    I am having a difficult time understanding why my circuit is not working.

    Any help would be GREATLY appreciated!! thank you

    I have attached the link to the schematic and images of my circuit...

    Wireless microphone schematic


    [​IMG][/IMG]

    [​IMG][/IMG]
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You can't build radio circuits (particularly VHF ones) on breadboard, I wouldn't expect it to work
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    As explained RF circuits on project boards are prone to problems.

    In addition it appears you have at least two wiring errors.
    The top left 10K [R1] is shorted out and Q1 base to R2 and C1 is in the wrong hole.??
     

    Attached Files:

  4. dave

    Dave New Member

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  5. JimB

    JimB Super Moderator Most Helpful Member

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    Have a look here:

    http://www.electro-tech-online.com/threads/a-dog-tracker.278/

    It is a piece which I wrote some time ago which shows how bad breadboards are at RF.

    Sorry, but built as it is your circuit stands no chance of working.

    JimB
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I see very old metal-case transistors in the circuit. Maybe they are the BC107 transistors that I used in my first job at Philips in 1967?
    Then the transistors are 44 years old.
     
  7. transistor495

    transistor495 Member Forum Supporter

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    Nope, the transistors are 2N2222A, written we can see.

    For an info, I've tried many transmitters like this on my breadboard :), but not to recommend.

    The thing is, if you want to compensate for the stray capacitance, at least the 33pf might be a variable one. L1 looks ugly, need re-winding for sure.

    Look this coil and compare it with yours :)

    [​IMG]

    Lots of wiring errors as like eric already pointed out. Study the breadboard configuration first.
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    In addition to the problems of the breadboard and the poorly made coil, why are you making the crappy FM transmitter anyway? Its performance is HORRIBLE!
    1) It doesn't have a voltage regulator so its radio frequency changes as the battery voltage runs down.
    2) It doesn't have pre-emphasis (treble boost) like all FM radio stations so the de-emphasis in all FM radios will make the sound muffled without high audio frequencies.
    3) It doesn't have much power so its range might be as far (or as short) as you can talk loudly.
     

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