FM kit tuning

Discussion in 'Wireless & RF Design' started by westwoon, Jun 18, 2009.

  1. westwoon

    Thread Starter New Member

    Jun 18, 2009
    Hi, audioguru, may I know how to change the output transmitting frequency for the BH1417? is it change the FM oscillator at pin 9 only? assumming I want to have 315Mhz.
    Last edited: Jun 18, 2009
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. Audioguru

    New Member

    Dec 20, 2007
    The BH1517 FM stereo transmitter IC uses a crystal-controlled frequency synthesizer.
    It is made to give four frequencies at the bottom of the FM band (around 88MHz) or four frequencies at the top of the FM band (around 107MHz). There is no way that it will work at a frequency as high as 315MHz.
  4. Kilian Caerwyn

    New Member

    Jul 4, 2009
    Many beginners wonder how Frequency Modulation is achieved in the basic one transistor circuit. One has to realize that the frequency of oscillation depends upon the Inductance in the tank coil and all the capacitance in parallel to it. This normally includes a 2-15 pF tuning capacitor plus a hidden component - the internal capacitance of the transistor. In low frequency circuits, one ignores the 2-20 pF internal capacitance of the transistor but you can see that it is important in 100 MHz circuits as it's value is of the same order as the tuning capacitor.