Filtering sine wave with square envelope

[shav]

Hi!

I have generated a sine signal with square envelope (signal for echolocation). My task is to add white gaussian noise, which I already did and then to filter the noise.
How can I filter the noise with this kind of signal? I tried Bandpass IIR, but it does not completely filter the noise.
Here are signal parameters:
Sine frequency: 5kHz
Square signal period: 0,2 s.

Below signal in time domain and the spectrum without the noise:


Below signal in time domain and the spectrum with the noise:

 

[FvM]

Filter bandwidth will be chosen in a noise suppression versus envelope rise time trade off. Apparently the filter parameters aren't well considered yet. The noise power looks unrealistically high, though.

 

[KlausST]

Hi,

Since you generate the frequency on your own... I'd use:
* either a lock in amplifier in the analog side
* or some kind of DFT on the digital side.

In both cases you get phase shift information to improve delay resolution...to measure distance

Klaus

 

[andre_luis]

The first thing that come to mind is to implement a filter with the same even components of frequency and amplitudes of a decomposed square wave (namely, Taylor's series), which may have been supposedly what you did, but it is not clear until which multiple of the fundamental your IIR filter have considered, and you did not show the graph with the result of the filtering that you did. In addition you did not mention the frequency of the carrier, wich should be also considered on the filtering as well.

 

[shav]

I don't think the way I filtered it was correct, but below are the results. I used 3th order Butterworth IIR bandpass (4900Hz-5000Hz) filter.



So as you can see, it is not what I would like to have. Sine does not have square envelope and the components related to (I guess) square wave still include noise. Below the zoomed graphs around carrier frequency (5kHz) of spectrum without the noise and after filtering.



Do you think there is a way to first somehow decompose the sine and the square wave and then filter then separately?