Get harmonics

[Benny.zhu]

     First, thanks to you see my question.

My question is that I want to get the second harmonics of the high frequency !

The  waveform from the oscilloscope, and this waveform is a 25KHz sine modulate on the 100Hz oblique wave.

The attachment is the csv file, include the waveform data.

[johnsold]

Your attachment did not appear.  Please try again.

If I understand you correctly you have a 25 kHz carrier which has been modulated by a 100 Hz sawtooth signal. You want to do something with the 50 kHz component?  What do you want to measure on the second harmonic? Is your sampling rate high enough?

Lynn

[Benny.zhu]

Hi Johnsold, thanks for you respond.

      I want to get the second harmonics of the 25KHz. And to get the frequency and amplitude.

The sample rate is 5 MHz.

[Henrik_Volkers · Accepted solution]

here is a quick try

However with 5Msample I see a 500k fundamental.... just change the samplerate and the search options to 250k, 25k and 50k ....

I used the extract single tone vi for this ...

And now please tell us what it is 😄

[Benny.zhu]

Hi Henrik

    Thanks a lot for you respons. I have been 3 days vacation.

I try to run this VI ,but i do not understand how to get the second harmonics of 25KHz.

I change the approx freq to 100Hz, it is nothing to show on the front panal.

And this VI(

Extract Single Tone Information VI

) is use for find the frequency in the specified frequency, so i change this to 25KHz ,50 KHz, but I got nothing. 

So, could you tell me which wave is the harmonics? 

[Henrik_Volkers]

The needed input for this vi is

the samplerate, (you should know it, but maybe you're wrong, see below )

the advanced search parameters for the two frequencies ( your frequencies (25k and 50k) and a search range expressed in % of samplerate 0.1%here )

and the number of periodes (something between 2 and 20), that parameter is used together with the first search frequency to calculate a windowlength (in sample) that is shifted over the data

The data you attached didn't match what you said about it 😉 , so maybe that's the reason why you don't get results.

Choosing the declaired 5MSPS I zoomed into your data and found that the sine on the ramp has a periode of  ~10 sample -> 500kHz, that's why I enter 500k for the approx frequency (and 1MHz for the harmonic) , you get the same graph (with different scaling) when you take the same data but enter 250k samplerate and 25k and 50k in the approx. freq fields.

Before poking around in the code, how do you get your data?

[Benny.zhu]

Hi Henrik

    I get this wave from oscilloscope.

[Henrik_Volkers]

So you how do you know the samplerate of the csv data? 

[Benny.zhu]

Hi Henrik

    Thanks a lot.

 I got it, the samplerate should be 500KHz.

[Benny.zhu]

The data is from my colleague, and he told me the samplerate.

So, how do you know the samperate is wrong? You do not answer this, I just curiousness.