Help with amplitude modulation

[WickedW4lker]

Dear Labview users, 

Im having some trouble with this Amplitude Modulation. What I want is to change the Amplitude of a sine wave using a rectangular pulse as following (see figure): 

The A.M. sinewave will be the input for my Daq device. I figured this is a strange modulation since i haven't found any info about this type of modulation (most only refer to sine-by-sine modulation). 

Any help on this problem would be greatly appreciated 🙂 

Regards, Dennis

[mikeporter]

Is the problem that you don't know how to do the modulation? The only strange thing to my eye is the relative frequencies of the two signals. Normally you have one (called the carrier) that has a much higher frequency. Also remember that as M. Fourier taught us a squarewave is simply the result of summing a very large number of sinewaves.

Mike...

[WickedW4lker]

Dear Mike,

Thank you for your reply! My problem is indeed that i dont know how to do the modulation =/

My drawing might be misleading. The carrier (which is the sinewave) is in fact between the rectangular pulse (AM-modulated by it) i haven't drawn that one because there is no sine function in paint 😛

Some additional information regarding the frequencys: 

- The sinewave is a typical mains signal with 50 Hz.

- The squarewave's amplitude will be increasing, starting from 0.008 Hz till 40 Hz.

So yes you are indeed right about the carrier frequency being higher..

Still, any help will be greatly appreciated 🙂

[DFGray · Accepted solution]

Amplitude modulation is simply multiplication.  If you multiply your sine wave carrier signal by your amplitude modulation you will be there.  There are a lot of subtleties, but that is the essense of it.  The wikipedia article is a good roundup and has some nice graphics to explain it.  In LabVIEW you can multiply two arrays as easily as multiplying two numbers.  Just wire them both to the multiply primitive.

[WickedW4lker]

Dear DFGray,

Yes i figured that out, but i was hoping that someone would come with a nice example ^^ 

Anyway, both of you thanks for the help!

[tbob]

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@WickedW4lker wrote:

Dear DFGray,

Yes i figured that out, but i was hoping that someone would come with a nice example ^^ 

Anyway, both of you thanks for the help!

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OK here is a nice simple example: