Electronic Circuits and Diagrams-Electronic Projects and Design
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FM transmitter using UPC1651

Description.
Here is the circuit diagram of an FM transmitter using the IC UPC1651. UPC1651 is a wide band UHF Silicon MMIC amplifier. The IC has a broad frequency response to 1200MHz and power gain up to 19dB.The IC can be operated from 5V DC.
The audio signals picked by the microphone are fed to the input pin (pin2) of the IC via capacitor C1. C1 acts as a noise filter. The modulated FM signal will be available at the output pin (pin4) of the IC. Inductor L1 and capacitor C3 forms the necessary LC circuit for creating the oscillations. Frequency of the transmitter can be varied by adjusting the capacitor C3.

Circuit diagram with Parts list.

fm-transmitter-using-upc1651


Notes.

  • The circuit can be assembled on a Vero board.
  • Inductor L1 can be made by making 5 turns of 26SWG enameled copper wire on a 4mm diameter plastic former.
  • A ¾ meter insulated copper wire can be used as the antenna.
  • Do not give more than 6V to the IC.
  • Mic M1 can be a condenser microphone.
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26 Comments

  1. Fahd

    I am thinking about building this circuit, but i require some evidence or proof about its performance results for my general satisfaction to start with. Can anyone here tell me about its working probability?

  2. Poacher

    Has anyone built this? Looking at the circuit, the tuned circuit part (L1 and C3) form a series tuned circuit which will exhibit it’s lowest impedance at resonance, thereby sending most of the output to ground.

    I must be missing something here (probably something very simple) but it looks to me like this circuit could never work.

  3. udayanga

    can we replace Mic M1 with a Audio input from a MP3 Player.

  4. Shahroz Shabbir

    Can u let me knw the actual value of inductor?

  7. Rakesh

    thanks for giving it. i have a doubt how to recollect the transmitted signal at the reciever side pls give ciruit of Rx
    mail id:rakeshd4d@gmail.com

  8. Seetharaman

    By removing R1 you remove the bias given to mic. 5Volt supplies + should get connected Pin No 1 of IC and negative to Pin No3.
    The L1 details are available in the notes as well the antenna ‘A’length.

  11. Andrew

    questions:
    1) if i remove R1, +5V will alimentate only the IC.I am right?
    2) where i put ground from +5V? at pin 3? in datasheet says at pin 3.

    thank you.keep up the good work

  12. Seetharaman

    Hi Andrew remove R1 and reverse the polarity of C1 and feed any audio information in place of M1.

  15. kashem ali

    How long the range of “FM transmitter using UPC1651”?

  17. seal

    hi i want to ask if somene have a complete scenatics of a fm bug thanks

  18. Sim Silas

    How can I get the UPC 1651 IC.Can’t get it in the local market,yet it correctly suits my project needs.”A powerfull CCT it is.”

  21. Seetharaman

    HiMoiz it will be around 150MHz with the recomended components.

  22. moiz

    hi,i want to know the operating frequency urgently.plz

  23. Doc

    the pdf for the chip..shows it’s a high uhf freq chip.
    19db @ 500megs..and just a few parts…looks interesting…theres a schematic of this with the 7805 voltage reg on 9v here on the site someplace..

  25. thilina

    i am going to make this. but i wanna know how long this will work.