Ok , I finally made the below circuit to oscillates and even resonate. It resonates in a range from 18 to 21 mHz depending on me moving the inductor . However , no matter how many inductors I replace , how many capacitors I change it just doesn't oscillates or just does it in the same range above mentioned. How is this posible ?.

 

You need a circuit with more sophistication to be as frequency agile as you seem to desire.

 

As Papabravo indicated the circuit is not very good and, actually it is terrible. Congratulations for getting to oscillate, but it is time to move on to a more reliable design.

Please have a look at this simple oscillator for the FM broadcast band. You may leave the microphone it’s load resistor and coupling capacitor out of the circuit if you wish.


https://www.hackster.io/makerrelay/fm-frequency-wireless-microphone-module-diy-kits-aee96a

 

For a stable mode of oscillation the circuit must have gain that exceeds the losses at the intended frequency. The circuit shown is indeed a poor design, and is not likely to ever work well.
The very first obvious flaw is that the tuned circuit is not directly tuned, which in this case insures instability. The circuit shown on the link is much better , but the link is obnoxious.
This circuit is in the class of what is often called "a blooper", meaning that in some constructed versions it may work, but the detailed explanation of exactly how it works is not clear.

 

T

For a stable mode of oscillation the circuit must have gain that exceeds the losses at the intended frequency. The circuit shown is indeed a poor design, and is not likely to ever work well.
The very first obvious flaw is that the tuned circuit is not directly tuned, which in this case insures instability. The circuit shown on the link is much better , but the link is obnoxious.
This circuit is in the class of what is often called "a blooper", meaning that in some constructed versions it may work, but the detailed explanation of exactly how it works is not clear.
[/QU

 

T

Thanks a lot sir, it explains a lot.

T

Thanks a lot sir.