audio amplifier for am transmitter

hi,

i am trying to design am transmitter for short distance to learn basic calculations of transmitter

AM TRANSMITTER

modulations type am modulations
frequency range 1mhz
voltage supply 12v
transmitting distance 80m-100m
audio frequency 20hz-20khz
antenna
low level modulated with linear amplifier

i know i need following circuit to make transmitter
audio amplifier circuit
Oscillator circuit
RF amplifier circuit
microphone

microphone ratings
frequency response 20khz
impedance 2k ohms

my questions
what is gain of audio amplifier for am transmitter
give idea to know how much gain is required and which stage is used for transmitter
single stage, two stage, three stage ....

please explain with mathematical calculations
i don't care bad quality of transmitter


thanks.................

There is no fixed formula for calculating the gain needed to modulate an RF signal. You have to amplify the small electrical voltage or current from the microphone to a strength that's sufficient to modulate the RF signal. So, the amount of gain necessary depends on the output from the mic and the RF power at the point of modulation. The output of a microphone depends on the sensitivity of the mic and the loudness of the sound it picks up, and may be anywhere from less than 1mV to 100mV. In broad terms, a mic signal may be considered to be of the order of a few millivolts.

Thus, the amount of gain needed depends on three factors:
1) The strength of the mic output.
2) The strength of the RF carrier at the point of modulation
3) Modulation index.

Thus, the amount of gain needed depends on three factors:
1) The strength of the mic output.
2) The strength of the RF carrier at the point of modulation
3) Modulation index.

microphone specifications(i am not sure consider only for mathematics)
frequency response 20hz-20khz
sensitivity 40db at 1hz
s/n ratio 60db
impedance 2k ohms

modulations index=max.audio amplitude/max carrier amplitude

how to know the strength of mics?
what is modulations index for this transmitter?

thanks for quick reply