Please help...i want to demodulate using envelope detector

[Eldokch]

the first signal is the modulated ASK signal..i want to use envelppe detector to convert it to the signal below it

how i can do that...i have tried the envelope detector in the sound and vibration toolkit but with no use

The first signal is bits passed through a filter then multiplied by a sine carrier

The second signal is the one i want to retrieve from the first signal using envelope detector

[Henrik_Volkers · Accepted solution]

Simplest way: absolute value and mean over one periode.

[Eldokch]

Thanks for your reply Henrik

but still i don't understand...where would i put my signal in this diagram

[Henrik_Volkers]

How much do you know about LabVIEW?

What is your background and what is your goal?

First I created my own AM signal (two sine blocks with wfrm output  (10k samplerate, 10k samples) )  and a multiplication ....

Can you find the absolute value icon?

the mean filter  over one carrier freq. periode is done by a convolution with a rectangular window (or array with a constant value) where the length of the window (size of the array) is ABOUT the sample point length of one carrier frequency periode.

I took the sample frequency(Fs) devided the carrier frequency and round it to the next full number ...

(homework:  How could the window be changed to match non integers?)

[Eldokch]

it's only my first week..i have to learn alot in a short period of time because of my bachelor

my goal is to send the signal..above..using USRP

and recieve the signal and using envelope detection i can recieve the second signal..and then transform from analog to digital

sounds simple enough..NOT 🙂

Thanks for your help

[Henrik_Volkers]

didn't the NI USRP package came together with bells & whistles (mean the LabVIEW  RF tools? mod&demod etc vis??)  AND a TUTORIAL??

[Eldokch]

yes it did but not with envelope detection

[James-B]

Hey Eldokch,

There is an envelope detection VI in the Sound and Vibration toolkit if you have access to that.  Otherwise, Henrik's code is good.  

The upper left half is generating the AM signal.  I believe you already have that part.  The bottom part cacluates the size of one period of the carrier wave for the convolution window size.  Then the bit of code on the right takes the absolute value of the waveform and averages it over the period.