problem in my Fm transmitter

Discussion in 'The Projects Forum' started by haithem alsaab, Aug 8, 2013.

  1. haithem alsaab

    Thread Starter New Member

    Aug 8, 2013
    12
    1
    Hello every body
    I'm glad to register in this forum it is one of the good forums that I've seen.
    Dears I have a project which is about creating a Fm transmitter I went to the shop and I find all the component except some capacitors
    that I fell to find it so I forced to create these value by adding capacitors in parallel or series
    this scheme of the project
    [​IMG]
    this is after the modification
    [​IMG]
    and this is real pic
    [​IMG]
    my question I'm I right when I replace the C
    the second question I fell to make it work and I really do not know why can you guess where is the problem
     
    Last edited: Aug 8, 2013
  2. #12

    Expert

    Nov 30, 2010
    16,320
    6,818
    You used the wrong kind of board to connect the parts. Use a printed circuit board.
     
  3. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    You can't build high frequency circuits on a breadboard.
     
  4. absf

    Senior Member

    Dec 29, 2010
    1,493
    372
    here is an example how you should layout your FM circuit.

    [​IMG]

    Allen
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,132
    267
    What you need to understand is that the solderless breadboard you are using has lots of stray capacitance between connections, imagine if you connected 10pf capacitors between every connection point, at 100 mhz this causes havoc.

    Also- at these frequencies, even the length of one jumper wire has significant inductance.

    Building RF circuits requires a totally different way of looking at layout and construction practice.
     
  6. haithem alsaab

    Thread Starter New Member

    Aug 8, 2013
    12
    1
    thank you all
    Thank you for your quick response. I really appreciate your
    so guys
    how can I use redesign ,so that it can work in this board even if I change the freq the important point is to make it work as an Fm trans ?
     
  7. Mussawar

    Member

    Oct 17, 2011
    68
    3
    There is another issue. Avoide using the combination of capacitors and resisters. RF circuits are very senstive so can't be assembaled roughly. Try to use the nearest available values. Best idea is to get parts from some old RF PCB (TV or Radio). You might get the exact values from here. Once I have made this type of circuit. Your coil would give you a relaxation. Changing the distance bw turns will change the freq so you can compensate the PF capacitor's values. Infect assembling the RF circuits need professional hands. Even a bad layout will mess up you circuit. If you can’t make a PCB, you can try this: Draw a PCB layout on a hard plastic sheet and drill it as it was a PCB. Now mount the parts and make connections by using a jumper wire exactly on the layout pattern. (I used this method for the first time and was successful). Q2 is the key portion of the transmitter. If you succeded to tune it somewhere in the entire FM range (88Mhz to 108Mhz) you got it. Rest of the circuit is just a Mic Pre Amplifier and would be easy to assemble. Wish you gud luck.
     
    Last edited: Aug 9, 2013
  8. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    You might want to have a look at the following PDF:
    rf_proto-1.pdf

    Bertus
     
    #12 likes this.
  9. haithem alsaab

    Thread Starter New Member

    Aug 8, 2013
    12
    1
    all guys above thank you very much
    really I'm proud to be with you
    In summary , I have to use a printed circuit board right ?
     
  10. #12

    Expert

    Nov 30, 2010
    16,320
    6,818
    That and a lot of education.
     
  11. haithem alsaab

    Thread Starter New Member

    Aug 8, 2013
    12
    1
    ok I'll work hard and hard until I beat you:D
     
    #12 likes this.
  12. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,132
    267
     
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