Is it like you use an AM receiver to receive FM?
I tried this with a commercial AM receiver. without good results.

 

can we use audio jack instead of condenser microphone??

 

The regen receiver oscillates all the time and needs a very strong radio signal to receive it. A regen receiver that works better has a regen control that is adjusted so it almost oscillates and is much more sensitive.

It is not a real radio circuit, it is very cheap and simple so of course it is without good results.

The signal level from a microphone is about 10mV but the signal level from an audio source is 300mV or more. What do you think is needed to replace the mic with a jack?

 

can we use audio jack instead of condenser microphone??

You might be looking for the current FM transmitter thread. It is at the link below.

https://forum.allaboutcircuits.com/threads/fm-transmitter-breakdown-analysis.142888/#post-1209966