RE:FM HETERODYNE TRANSMITTER

Discussion in 'General Electronics Chat' started by NKEONYINYE, Nov 29, 2008.

  1. NKEONYINYE

    Thread Starter New Member

    Oct 25, 2008
    2
    0
    Hi Senior Member Bertus

    Please,I am was confused at some of the stages as follows:(1) The stage coupled directly to the VFO: Please is this an IF amplifier or a buffer? The limited literatures I have been able to contact show that a VFO's output is coupled to a buffer (unity gain but I calculated the gain of that transistor circuit and got 2.36.(2) Is the last circuit before the PA an RF amplifier? (3) I have not been able to find a 10.7MHz IF transformer but it seems to me that the IF transformer acts as a filter as well as a “coupler”. So can I replace it with a filter circuit and in what way (the circuit diagram)? What effect will it give to the transmitter? (4). I was not able to get a 44.9333MHz crystal but a 47.5MHz crystal. Can I use this and if yes, how can I finally achieve the same 145-146MHz transmission frequency.(5) Please what are the inductance values of the coils (L1-L3 and T3), or, with what wire gauge and core diameter were the turns achieved.

    Please the link to the FM heterodyne transmitter I am refering to are as follows: http://forum.allaboutcircuits.com/showthread.php?t=13137&highlight=heterodyne+transmitter


    http://web.telia.com/~u85920178/tx/fm-tx1.htm
    I sincerely appreciate you all.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,641
    2,344
    Hello,

    Here is the original schematic you are refering to :

    [​IMG][​IMG]

    In the origenal versrion L1 is tuned round 10.7 Mhz.
    This is mixed with 3 X 44.933 ( ca 135 Mhz ) , the result is 145.7 Mhz.

    In you case the mixing frequency will be 3 X 47.5 ( ca. 142.5 Mhz ).
    To get in the 144 - 146 range the oscillator must be 1.5 Mhz - 3.5 Mhz.
    So you will have to change the circuit round L1 and T1 to get it working.

    Greetings,
    Bertus
     
    Last edited: Dec 6, 2008
  3. NKEONYINYE

    Thread Starter New Member

    Oct 25, 2008
    2
    0
    Thank you so much for the answer

    Regards
    NKEONYINYE
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,641
    2,344
    Hello,

    I have recieved a PM that you can not find some parts.
    I think all the parts can be ordered at BOX73 ( www.box73.de ).
    They also have the original crystal used in the transmitter.
    I have attached a PDF with the RF parts page from the magazine FUNKAMATEUR ( www.funkamateur.de ).

    Greetings,
    Bretus
     
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