[QUESTIONS] Modulation Index

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oasis4355

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Hi all,

I'm constructing this FM transmitter.
**broken link removed**

I would like to find out the modulation index of this transmitter. Can someone please advice me?

Just another questions. If we change the modulation index, can we still obtain back the same audio signal in the reciever?

Thanks in advance

Jason
 

FM modulation index is = (peak frequency deviation / modulation frequency)

This schematic use a reactance modulator. When the modulating signal is applied to the base of Q1, the emitter-to-base bias varies at the modulation rate.

In this case the modulation index depends by the emitter-to-base reactance, by the Q of the LC tank circuit (L1, C2, and C3) and depends also by the modulation frequency.
 

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