Need help to solve the problem i facing.
Design requirement. Fo = 90mhz . Modulation index of 5.
Below circuit is designed using ADS.
At first i just simply assume my varactor is biased at 2V and then i use formula to calculate the require inductor value to achieve carrier frequency of 90Mhz.
Additional info, i am using MV2109 varactor and 2N3904 NPN transistor to create oscillation also mixture.
Here is the problem comes i, want to connect my microphone as input and it must compatible with the varactor to achieve whole system having modulation index of 5.
I am stuck at this requirement. Hope you guys can give me idea how to achieve it.
2. Continue question, what kind of microphone should i consider to apply ?
3. Do i need to have good low pass filter to prevent my carrier frequency load to my microphone or DC source?