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- 14th July 2010, 12:47 #1

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## What is the modulation index ?

Ok just some very simple Qs first

1. What exactly is the modulation index? Is it equal to Max amplitude of modulating signal / Max amplitude of carrier signal?

2. Do we have to normalize (Make the amplitude equal to 1) every modulating signal before we use it in our calculations? If so, how do we normalize signals with more than one component? Ex - 2Cos(2πf1*t) + 3Cos(2πf2*t)

3. After a modulating signal is normalized do we still say the modulation index = Max amplitude of modulating signal / Max amplitude of carrier signal (Using the original values of the amplitudes) when we are doing our calculations or just say it is equal to 1 / Max amplitude of carrier signal?

Thanks

- 14th July 2010, 12:47

- 14th July 2010, 17:57 #2

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## Re: Amplitude Modulation

1) No. Modulation index indicates how much the carrier's amplitude can change due to modulation. For example, we have a 1V carrier wave:

With 50% modulation, the carrier's amplitude can be changed from 1V to 0.5V

With 100% modulation, the carrier's amplitude can be changed from 1V to 0V

Check the site for more info:

http://en.wikipedia.org/wiki/Amplitu...dulation_index

2) No. When dealing with multiple harmonics, the modulation result will be a signal with multiple harmonics as well. Therefore any calculations must be done separatelly for each input harmonic. Each harmonic should be treated has a single input signal and in the end the several output signals should be summed.

3) Question 3 is answered by question 1. Modulation index does not account for input signal's amplitude__directly__.

- 14th July 2010, 17:57

- 11th August 2015, 18:56 #3

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## Re: What is the modulation index in Phase Modulator?

What is the physical interpretation of Mod. Index in Phase Modulator?

Mod. Index=1 Radian the what is it represents ?

Is it represent 100% of carrier Phase is modulated ?? am I right ?

what meant by Direct Phase Modulator ?

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