NI PXI-5105 FSK Demodulation

[plasmaphase]

I'm able to sample an FSK waveform (2MHz and 1MHz carrier frequencies with a 115200 baud signal) with my PXI-5105 Digitizer.  I'm now trying to demodulate that signal back into a binary stream.  Below is an image showing my front panel.

I originally wanted to use the Modulation Toolkit FSK demodulation block, but I then noticed it (I believe) requires IQ, and is used with the RFSA blocks.  What's the best way to go about decoding this FSK signal back into binary?  Below is my block diagram.  I've also attached my VI (requires Modulation Toolkit).  Any help is appreciated, thanks in advance!

[Marcus_M]

Hi,

You are correct. The "MT Demodulate FSK VI" requires an input of "Input Complex Waveform" that is defined as t0 (start time), dt (time interval), and Y (complex-valued signal-only baseband modulated waveform, i.e. IQ data). You can however use this VI with your 5105 and not be required to use any of the RFSA VIs. If you go into the LabVIEW example finder then go to Toolkits and Modules>>Modulation>>NI-SCOPE (High-Speed Digitizers)>>MT niScope Bursted FSK.vi you can use this example to acquire FSK data and demodulate it to demodulated bits only using your 5105 and not using RFSA VIs.

Regards,

Marcus M.

[plasmaphase]

I have modulation toolkit 4.3.3 installed, and see that block, however, when I try to load it, it asks for "CPM System Parameters.ctl"  Where would I find this?

[plasmaphase]

I'm using LabView 8.6

[Marcus_M]

Hi,

You should be able to find that file under this file path:  C:\Program Files\National Instruments\LabVIEW 8.6\vi.lib\addons\Modulation\Digital\Support\Controls

I've also attached the file in case you don't have it.  

Regards,

Marcus M. 

[plasmaphase]

It's really not intiutive to me how this VI is configured.  I'm doing FSK using a 500kHz and 1MHz sine wave which contains a 115200 baud stream of data containing 0x52 repeated continuously.  I've tried all the obvious settings with no luck.  Any suggestions?  Thanks in advance.

[MikhailK]

Hi plasmaphase,

What kind of results have you observed after running "MT niScope Bursted FSK.vi"? Were there any errors when you ran the code? What "obvious settings" have you set? Please send a screenshot of the front panel. You should disable "Attempt to sync" and set the carrier freq. to 1MHz and the sybmol rate to 115200 baud (symbols/second). How many symbols do you have in your burst? Is it finite or continious? How are you generating FSK modulated signal?

Regards,

[plasmaphase]

Here's a screenshot:

[plasmaphase]

My FSK is continuous.

[MikhailK]

Hi,

MT Demodulate FSK requires both the pulse shaping filter used in transmission, and the
"modulation samples per symbol" and "demodulation samples per symbol" should both match the "samples per symbol" in the FSK system parameters.From the screenshots that you posted in your first and last posts, those parameters do not match 128 != 32. I presume you have modified those since then. What are your mark and space frequencies? Can you also post the Power/PSD vs. frequency graph (FFT Power spectum vi) of the acquired signal and also confirm that you can see your mark and space frequencies in the spectrum of the acquired signal? What is the bit pattern that you are sending and what bits do you get on the receiving side?