FM modulator direct method

[ericyeoh]

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?

 

[audioguru]

Your schematic is a nightmare to read since it has text and dots all over the palce.
Your varactor diode has a very small tuning ratio so stray capacitance must be kept to a minimum.
The tuning coil has too much resistance in series.
A microphone has a very low output level so usually it has a preamp with lots of voltage gain. An electret type of mic is used today.
Here is a circuit that is similar to yours. I don't know if it works:

 

[ericyeoh]

The value of tuning coil resistance is just the assumption to represent actual resistance exist with the induct or.
Yup, in fact during early stage, i refer your mentioned schematic as a start point.

I am now confusing on how to link the resonator part to the mic in order to hit the project requirements.

 

[audioguru]

I am now confusing on how to link the resonator part to the mic in order to hit the project requirements.

It is your choice:
1) Scream into the mic.
2) Or add a mic preamp.