Frequency and Power measurement

[MVK]

Hello Andy,
I am having a UUT (unit under test), which is transceiver. It can able to send and receive RF signals. My requirement is to measure Frequency Error and Carrier Power of the signal, which is coming out from UUT without doing demodulation. I am having NI RF measurement device PXI 5660. Already I have done a small application to measure these two parameters. But the thing is I am not sure about my application will it goes in right way or not? But the situation is, I don’t have UUT with me right now. For that case what I am trying to do means, I am having PXI 5670 using this RFSG, generating some RF signals like sine wave with 25KHz at 5dBm.
Mr. Andy can you give me some suggestion for above mentioned process?
And one more thing there are two Signal configuration VI’s namely ni5660 Configure for IQ.vi and ni5660 Configure for Spectrum.vi. Out of these two which one should I use? To measure carrier power I should use ni5660 Configure for Spectrum.vi. But other case what can be done?

Note: I have enclosed a Zip file which is having three VI’s. One for generate a RF signal using 5670
Another two for Frequency error and carrier power measurement respectively. For your info please find the attachment.

[Alan_L]

Vijay,

I did not find the attachment you mentioned in the text of your post. However, you are definitely on the right track. To perform both of these measurements you'll configure RFSA for "Spectrum." In the case of frequency error, you can do a peak search on the resulting power spectrum to determine the primary frequency component of your signal. Of course you could do further analysis to find other frequency spikes.

I hope that this helps to point you in the right direction. Please let me know if you have further questions.

Thanks,
Alan L
Applications Engineer
National Instruments

[MVK]

Hello Alan,
Thank you for your reply. Sorry unfortunately I forgot to attach file. Now I have done it so please find the attachment.
Mr. Alan I want to find out Modulation depth for AM (in %) and also for FM (in KHz). I have seen some example to find out Modulation depth for AM signal but my doubt is whether is it correct or not? Why because, “ The Depth of AM is the ratio of the amplitude of the modulating signal to the amplitude of carrier” am I correct? So if I try to correlate my above definition with the example code the way that VI find modulation depth is not exactly correct. So please explain in detail according to my definition please.

(Note: In that example, a vi called ‘Extract Single tone Information.vi’ giving a output named as ‘detected amplitude’ which is multiplied with 100, then that result indicated as a ‘Modulation depth’.)

And also I want to find out modulation depth for FM signal. Can you give me some idea to do coding for this or else if any ready made vi available in this same please send it across to me.

Note: I have attached a zip file which is having vi's. Three vi's for previous enquiry and fourth vi 'modulation depth' is for this enquiry.

[RossC]

Vijay,

Alan is not in the office this week. I sent him an e-mail about your question, so hopefully he can advise you when he returns. Have a good day!

Sincerely,

Ross C
Applications Engineer

[Alan_L]

Vijay,

Hi! I apologize for the delay in my response, but as Ross mentioned I was out of the office last week.

You are correct that the definition of modulation depth appears to be different than the implementation in the example you found. However, under the hood, the example is returning correct results. Since the SubVIs are not password protected, you can dig into their block diagrams and take a look at exactly how they are implemented. You can also read a more formal definition of modulation depth by clicking HERE.

While there are no examples for FM modulation depth that I can find, the coding will be very similar as for AM since the underlying principle (as discussed in the link above) is the same.

I hope that this is helpful to you!


Thanks,
Alan L
Applications Engineer
National Instruments