complex waveform and FFT

[kantabra]

Hello everyone!!

I'm using the MT RFSG Generate PSK.vi that you can find in the examples menu of LabVIEW. I get a good singnal because I see it in an Spectrum Analyzer, but now I want to see the same signal but in the LabVIEW. The problem is that the vi has an output which name is "complex waveform" and I don't know how get the graph from that output. I know that I must use the FFT to obtain the spectrum but isn't directly so I don't know how to do it. Have I to use some vi between the generate PSK. vi and the FFT.vi?? How could I do it?? What FFT.vi is the best for my problem? I need help.

Thank you.

[johnsold]

I do not have the modulation toolkit so I am not sure what the complex waveform is.  The standard FFT.vi is polymorphic and will accept an array of complex numbers as an input.  Many of the spectrum VIs which take waveforms as input use the FFT.vi internally so they may be able to accept complex waveforms.  The detailed help for the Extract Multiple Tone Information.vi explicitly states that it can accept complex waveforms.

Graphs can accept complex arrays although they only plot the real part.  To see both parts use the complex to Re and Im or complex to r, theta functions.

Lynn

[SimonD]

Hi,

The MT RFSG Generate PSK use I/Q data. It's a complex representation with the In phase signal and the Quadrature signal. This complex waveform can be used directly with a fonction like FFT Power Spectrum.

[kantabra]

I'm trying use directly my complex waveform with the FFT Power Spectrum and it does not work. I've connected the complex signal in the time input (and in the others) and nothing....

[SimonD]

Can you post your vi?

[kantabra]

Yes, of course. I want see the spectrum of the complex waveform that is and output of the Continuos BB-PSK Generation.

[SimonD]

OK, it's because the output of this vi is a typdef (ComplexDataWaveform.ctl), not a waveform. You can try something like that:

You can extract your data from the typedef cluster and build a waveform.

[kantabra]

With this solution It still doesn't work. If I connect the output complex waveform with the "get waveform componentes.vi appears a error message that says: you have connected two terminals of different types. The type of the source is typedef complex data waveform.ctl cluster of 3 elements. The type of the sink is waveform (dbl).  

[SimonD]

Yes, you need to use unbundle cluster instead of get waveform compenent. It's because your output is a typedef cluster (named 'complex data waveform') and not a waveform. 'waveform' is just its name, not its type.

[kantabra]

Thank you very much, now it works perfectly. I would ask another important thing for me. In the NI-RFSG Configuration Mode, in the option generation mode I choose a continuos cosaine but I don't know which are the parameters of that cosaine. I would like plot this signal and see it. Is that possible???