I came across this FM transmitter circuit whilst searching for 27Mhz transmitter/oscillators :
I have seen several versions of this in my search. The documentation states it will transmit in the 88MHz to 100Mhz fm band.
I cannot see how the front end manages to modulate the transmitted frequency. To me it looks like the output of the audio amp (Q1) modulates the base of the Q2. Q2 is in common base so modulating the base will just shift the bias and change the gain. Changing the gain modulates the amplitude not the frequency.
I'm just starting to learn rf oscillators, they have always been a mystery to me so any help would be appreciated.
Thanks
Garry
I have seen several versions of this in my search. The documentation states it will transmit in the 88MHz to 100Mhz fm band.
I cannot see how the front end manages to modulate the transmitted frequency. To me it looks like the output of the audio amp (Q1) modulates the base of the Q2. Q2 is in common base so modulating the base will just shift the bias and change the gain. Changing the gain modulates the amplitude not the frequency.
I'm just starting to learn rf oscillators, they have always been a mystery to me so any help would be appreciated.
Thanks
Garry