real time signal analyzing

[george2309]

Hi everybody,

I am a new member here and generally new with Labview.

I am a student and I am running my diploma project which is a construction of a Doppler radar for velocity measurement of a pendulum. I am using 9 GHz signal generator and I am working with wave-guides. Using a power devide T-Type  H-plan, i get the signal of the doppler frequency (difference between the propagated signal, and the signal that arrives to the receiver horn which contains doppler shift). then with a crystal detector and through a coaxial cable I can transfer the signal to the oscilator or to the pc using NI PXI-6281 card.

-My first goal is to make the power spectrum of the signal and find the highest peak frequency which corresponds to the highest velocity of the pendulum. 

- Final goal is to build a real time graphic wich contains the velocity of the pendulum related to time.

-Until now I have done the attached file but the power spectrum is showing alaways a peak around 34000 (maybe because if the noise) no matter how fast the pendulum is moving (I am also using low pass filter because because of the computer inserts a lot of noise).

-how can i calculate the real frequency (X-scale) to the power spectrum?

-Do you have any ideas how can i build the graphic of the velocity related to the time?

P.S

I have been based on this video

https://www.youtube.com/watch?v=xMWIATas_e0

Thank you a lot in advance!

[Lemongrab]

Hello George2309,

It would be easier to understand what you are trying to do if you would post some screenshots of your graphed data after running the VI. But from what I can currently see, you are performing a filter to remove noise from your signal. However you are not calculating the power spectrum from the filtered signal, so that noise is still present in the power spectrum. I recommend using the filtered signal as the source signal for calculating the power spectrum, so the low-pass filter removes high frequency peaks like the 34000 peak you have mentioned. Give this a try and let me know what the results are.