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help in making fm transmitter??

Discussion in 'General Electronics Discussion' started by ssng.89, May 19, 2011.

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  1. ssng.89

    ssng.89

    1
    0
    May 19, 2011
    we were making a fm transmitter from the linkf as follow
    http://www.electronics-circuit.com/basic_FM Wireless 3VDC.html
    but from the circuit we didnt get the 8turns inductor...so the shopkeeper gave a wire and said to make 8 turns from it....so my question is ..is there any specification to make it in 8 turns(i mean die of the circle and so)??and how to decide the value of the 8 turn inductor in henry from the circuit??

    one more thing for antenna he gave a simple looking wire...is ther any specifications for antenna too....
    please do reply us....as soon as possible ...so that we can carry on with the process. plzzzzz
     
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    The coil looks to be about 4mm diameter, put a 4mm drill bit the wrong way round in a hand drill and wind 8 turns. You could get a more accurate estimate by scaling your photo, knowing the size of the transistor. There are equations giving inductance for a specific design (try Wikipedia)
    The inductance can be calculated from the equation F=1/(2*pi*(sqrt(L*C))), chose a capacitance of about halfway on your trimmer. The inductance should be not too critical since the frequency can be trimmed over a fairly wide range with the trimmer.
    The antenna connection will affect the frequency and I assume that the coil (L2) is there to make the antenna resosnant at a quarter wave.
     
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