AM demodulation--> get envelope as well as carrier

[ashwini1]

am demodulation

Hi,

I am working on AM modulation. At receiver end i want to separate my modulating signal with carrier signal. (i want to have both the signals available after demodulation.)

Is there any way, where i can get back both the signals.

Thanks !
Ashwini

 

[mowgli]

demodulation of am

To demodulate an AM signal you can use the formula
sqrt(I^2 + Q^2)
where I,Q are In phase and quadrature components.
Then extract the dc component of the signal (= LP filter) which is related to the carrier amplitude.
For suppressed carrier you could extract the dc component directly from the envelope of the modulated signal.

Regards
Mowgli

 

[FvM]

determining the am envelope

Your answer reveals some lack of clarity in the question. I guess, that ashwini1 intended to extract the carrier signal rather than the amplitude value.

PLL is a versatile technique to extract the carrier. In case of the supressed carrier modulation mentioned by mowgli, it can't be recovered unless the modulation signal has particular known properties.

 

[ashwini1]

demodulation envelope am signal

Thanks for all the replies ..

The basic intention is to calculate the modulation index or percentage modulation at receiver end. When i go with normal am demodulation i.e., multiplying with carrier signal and apply LPF of carrier frequency to it so that i can get the scaled modulating signal. But the problem which i am facing is that due to dc component present in demodulated signal i am unable to calculate the correct modulation index. THis may due to improper filtering and if i filter with highest order my signal level will be of order 1e-15.

So i thought that, if i get carrier signals back at my receiver i can calculated the dc shift due to it and subtract the same from demodulated signal.

If there is any other better way to get back the original signal in more faithful way plz tell me and that is appreciated .

Thanks,
Ashwini