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.

 

We encourage placing new questions into their own threads, rather than hijacking existing ones.
This is the original thread - http://forum.allaboutcircuits.com/showthread.php?t=22411

 

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.

 

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.