Modulated signal with noise

[kabuto15]

Hi.
I've got current signal (very long) from ac motor. It's look like AM modulation. I want to find his envelope, but some noise are trouble here (FFT is ok). How I can (digital) cut off this noise ? Maybe some filter ?

 

[JoannesPaulus]

you need to low-pass filter the signal to remove the high frequency glitches.

 

[kabuto15]

Thanks for reply, but this signal is after LP. It's very long signal - about 5s and the carrier is 50Hz (AM). Spectrum is shown below

 

[karesz]

Hi,
Than you need a really better filter, or a plus notch filter for 150Hz!
K.

Added after 1 minutes:

You can set a pole/zeros better to eliminate the 3.th harmonics...

 

[karesz]

Hi mathuranathan,
Its true, I checked repeatedly the pic, it has a line at ca. 5Hz_is knowed the origin of that, is it a real signal pls?
If yes_of course, a bandpass is wished, but 50Hz is relative bulky_or need sinthetyc inductances/multiplyd capacitors or even gyrator circuit...
K.

 

[kabuto15]

I'm working in LabView so I can use any filter (any order) I want. The problem is when I use a bandpass filter (for example Chebyshev, 7th order, low cut off freg 30Hz, high cut off freq 70Hz) the signal has weird noise still.

It isnt normal AM modulation, so maybe I should find other way to cut noise. Maybe some digital image processing algorithm ? Median filter or something else ?