I'm student and I'm working on a school project. The project is a radio transmitter.
My question here is only about the frequency modulator part.
Here is my circuit :
Here is my output signal (blue) and input signal (brown) :
As you can see there is no modulation what so ever.
According to my teacher, my output should look something like this if my oscillating frequency is 93 MHz and my input signal is at 9.3 MHz:
My oscillating frequency is supposed to be 93 MHz. Here is how I did my calculations:
The *1.3 is just to make sure I respect the Barkhausen criterion
Do you guys have any suggestions to get an output at 93MHz when I input a signal at 9.3MHz?
Edit : I know the oscillating frequency can be calculated with the formula above but how can one theoretically calculate the amplitude of the oscillation and what affects it? I'm guessing RC and RL. Any suggestions?
Best Answer
First of all thanks to @BrianDrummond, @Andyak and @Leoman12 !!
This is my circuit now :
This is my transient :
As you can see it now oscillates. Theres is a DC component on the Vout but it goes away with time. Its hard to simulate because it would take a while with Orcad (my software) and a high resolution (low max step size).
So the key points were to :