topic Re: how to detect envelop of signal ? in Mathcad

how to detect envelop of signal ?

Mathcad111 — Tue, 17 Jul 2018 01:35:20 GMT

How to find upper and lower envelop of the signal ? please check my mathcad file !

Re: how to detect envelop of signal ?

-MFra- — Sat, 26 May 2018 12:57:53 GMT

Hi,

The noise's maximum amplitude is ten times higher than that of the signal. How to distinguish a signal from such noise? it's impossible!

Re: how to detect envelop of signal ?

terryhendicott — Sat, 26 May 2018 13:30:15 GMT

Hi,

You must break the signal into segments and find minimum and maximum of each segment.

Re: how to detect envelop of signal ?

terryhendicott — Sat, 26 May 2018 14:19:05 GMT

Hi,

Sorry a mistake in the lower envelope is corrected here.

Re: how to detect envelop of signal ?

LucMeekes — Sat, 26 May 2018 14:36:40 GMT

It's not entirely impossible. A lock-in amplifier will allow to detect signals that are below the noise level. Problem is you have to know the frequency you want to detect.

The OP's problem is extremely simple as posed, but I guess he's got a more fundamental problem (doesn't know his signal and which part of it is noise).

Luc

Re: how to detect envelop of signal ?

LucMeekes — Sat, 26 May 2018 14:40:42 GMT

That's extremely simple. For the problem as posed the lower enevlope is XT, the upper is XT+1.

But I guess that's not what you're after. What do you know about your signal, and what exactly are you after?

Note that Terry showed a way to estimate the envelopes, but do you need the envelopes, or are the envelopes just part of your way of what you really want to know about the signal?

Success!

Luc

Re: how to detect envelop of signal ?

Werner_E — Sat, 26 May 2018 15:01:16 GMT

Would this help?

You may play with the windows size (I have chosen 😎 and may notice some sensibility wrt the guess values of genfit.

Re: how to detect envelop of signal ?

Werner_E — Sat, 26 May 2018 15:11:15 GMT

You may also use your way of defining the signal for genfit.

The sensibility wrt the guesses and the window size remains though.

Re: how to detect envelop of signal ?

-MFra- — Sat, 26 May 2018 17:03:34 GMT

If the given signal is sampled, a digital notch filter tuned to the frequency of the signal should be used in such a way as to attenuate only the carrier while the noise is emitted at the output. To have the envelope a peak detector is added with a capacity ...........

Re: how to detect envelop of signal ?

-MFra- — Sat, 26 May 2018 17:06:50 GMT

This is not an answer to your problem. However, can the following analysis help you?

Re: how to detect envelop of signal ?

Werner_E — Sat, 26 May 2018 18:17:24 GMT

Maybe this old thread could be of interest, too:

https://community.ptc.com/t5/PTC-Mathcad-Questions/Phase-Shift-Problem/m-p/15134

Re: how to detect envelop of signal ?

Mathcad111 — Mon, 28 May 2018 05:19:08 GMT

Thank you for the effort could you please upload this mathcad file (of this program) ?

Re: how to detect envelop of signal ?

Mathcad111 — Mon, 28 May 2018 05:34:05 GMT

Thank you for reply,could you please explain bit more about what you doing (p1, p2) and i have posted some question regarding noise value please check my mathcad file once !

Re: how to detect envelop of signal ?

Mathcad111 — Mon, 28 May 2018 07:05:25 GMT

yes it's interesting but it shows some error " D=READFILE(files, "delimited") " is not working !

Re: how to detect envelop of signal ?

-MFra- — Mon, 28 May 2018 08:10:48 GMT

Hi,

Attached is the file with the graph with three cursors to read the values of the frequencies and the amplitude in dB

Re: how to detect envelop of signal ?

Werner_E — Mon, 28 May 2018 08:09:59 GMT

You would have to download the data files from the OP as well and put them in the correct subdirectory.

Re: how to detect envelop of signal ?

Mathcad111 — Mon, 28 May 2018 08:26:57 GMT

ok got it! in your file('WE_20180526_mathcad_ques-1') you have used 't' (which is basically belongs to transmitter end) but in the receiver side i don't have any idea about the time, for example if i know the exact time than i could able to find the frequency and i can used to reconstruct the 'Tx' signal, but the problem is, i don't know the exact time. could you able to do without the 'Transmitter time 't' ' (like approximation of that time).

Re: how to detect envelop of signal ?

Mathcad111 — Mon, 28 May 2018 08:35:05 GMT

thank for the file, but is it possible without the help of cff or fft ? and please consider this, in receiver side, i have no idea about the freq of the signal and time too what i have is only the data (like RX=[2,3,4.5,...so on])!

Re: how to detect envelop of signal ?

-MFra- — Mon, 28 May 2018 09:07:36 GMT

cfft calculates the discrete Fourier transform of the signal placed as its argument. Obviously it does not know the frequency of the sinusoidal signal that you add up. Even the spectrum graph does not depend on f, in fact, as you can see in the following figure, I have set f = fr = 1MHz.

Since the amplitude of the noise is too high, the signal is indistinguishable, even with a PLL you will not be able to find it.

Re: how to detect envelop of signal ?

Mathcad111 — Mon, 28 May 2018 09:21:06 GMT

Yes i understand that but how to calculate without CFFT ?