Signal-to-Noise ratio from Power Spectrum?

[rf curious]

Hi,

I have a feeling this is a basic issue but for some reason I'm not getting it.  I hope this forum can help.

I have a Power Spectrum (freq on the x-axis and power on the y-axis) and I am trying to determine the signal to noist ratio of the rf signal live.

I am using LV 8.5 and have the spectrum toolkit and am using an RFSA in a PXI chassis.

Any suggestions?

Thanks

- rf curious

[Yardov]

Hi Rf Curious,

This questions does not have a simple answer but let me share my thoughts and you can decide what it makes most sense for your application. For signal to noise ratio (SNR) you should have ideally the power of the signal and divide it by the power of the noise. The problem here is that you are looking at both at the same time (rf live signal). Depending of what type of signal is it, you can recreate it and substract it from the spectrum (you will need to recreate the phase and magnitude and delete it from the phase and magnitude of the spectrum). This is normally done with simple signals such as a tone.

If you don't have access to the magnitude and phase of the data, and you only see the spectrum, then you will have to do things different. You can probably measure the power of the signal by measuring the power of the band where the signal is located. Then, you can terminate your input and measure the power of the noise of the instrument (with same attenuation and RBW settings) and have a rough estimate. This method should have better results when S >> N. You can also take the adjacent channel (or further) noise reference.

Finally, if your signal has a pretty flat spectrum, then you can only take the difference between the noise and the signal since they both have the same RBW.

If by now, you have found other methods, feel free to post your ideas here for any other person that come across this problem.

Regards,

[Kumarz]

Hello rf curious

I want some info to setup spectrum analyzer to calibrate the power at receiver.
How can I measure the singal-to-noise raiton (SNR) of a signal using spectrum analyzer or oscilloscope?

Looking forward for your useful suggestions ...

Thanks,

[Brandon_B]

Hello Kumarz,

So exactly what kind of hardware and software are you trying to use?  The reason being, performing this type of analysis can vary greatly depending on whether or not you are using LabVIEW or C code and also depending on what the actual product is.

Have a nice day,

[Yardov]

Hi Kumarz,

I want some info to setup spectrum analyzer to calibrate the power at receiver.

 Did you mean, power at the transmitter? Or you probably calibrating a "different" receiver and want to make sure that your transmitter has enough SNR.?

How can I measure the singal-to-noise raiton (SNR) of a signal using spectrum analyzer or oscilloscope?

 Read my previous post and let me know where do you need more information. As I said, SNR measurement is not a straight forward answer.

Regards,

[Kumarz]

Hello

My source is a device working on 2.4GHz, I have attached an antenna to SA - 
I can see the frequency spectrum of the signal - with default parameters (i.e. RBW, Attenuation, span, sweet time etc). 
how can i figure out the SNR from that signal? 
& how can i change the SNR on SA? 

Thanks

Regards,

Kumarz 

[Chris_W.]

Hi Kumarz,

Gerardo has mentioned some good suggestions in his previous post. 

---

"you can probably measure the power of the signal by measuring the power of the band where the signal is located. Then, you can terminate your input and measure the power of the noise of the instrument (with same attenuation and RBW settings) and have a rough estimate. This method should have better results when S >> N. You can also take the adjacent channel (or further) noise reference.

Finally, if your signal has a pretty flat spectrum, then you can only take the difference between the noise and the signal since they both have the same RBW."

---

Also here is a developer zone tutorial that provides an equation for the actual calculation of the SNR. Also, here is an example that makes those and other measurements on simulated signals.

To modify the SNR, you can change the RBW. You can also feed your signal through an attenuator, though this might not actually change the SNR depending on what your signal is. 

Chris W

[RF_Buzzer]

Hi Chris,

The LINK which you provided is DEAD. It justs takes us to the MAIN DEVELOPER ZONE Page... and after searching for sometime, we are lost.

I would appreciate if you post the WORKING TUTORIAL LINK

"http://zone.ni.com/devzone/cda/tut/p/id/1949"...Since this is not working

along with the EXAMPLE LINK.

Thanks,

Dharmendra

[Chris_W.]

Hi,

You know to be honest, I don't remember what the original link that I was going for a year ago was. I can't seem to find it anymore. HERE, however is another developer zone tutorial about signal to noise ratio in depth. There is also a good document HERE that talks about making RF power and frequency measurements with NI hardware.

The examples that I was talking about is actually a shipping example that installs with the Spectral Measurements Toolkit, which you can get to by going to Start»Programs»National Instruments»Spectral Measurements»LabVIEW Support»LabVIEW XXXX Spectral Measurements Examples and then going into the folder named "Simulation." This will allow you to take a look at the SMT ACP (simulated).vi, which is an adjacent channel power measurement that is similar to what Gerardo mentioned above.

I would however take Gerardo's previous advice and measure the power of a tone when you have that input to your VSA, and then remove the tone and measure the noise power of the system and compute that ratio manually. 

Chris W

[qqa]

Hi every body

any one can help me to find the signal to noise ratio of the attached signal, and how to convert it to frequency domain. I know it is easy but it is not working with me since the power must have a main amplitude at the fundamental frequency which is 1Hz and I cannot find any component there.

Any help is appreciated

qqa