topic Re: FSK demodulation using ddc in RF Measurement Devices

FSK demodulation using ddc

Jdttang — Wed, 27 Jul 2005 19:14:26 GMT

At my university we have a PXI-5660 and want to demodulated real-time

an FSK signal with a carrier frequency at 915 MHz and a deviation

of 10 kHz. I guess we need to use the ddc for real-time operation. Is

there example program to get us started ?

Thanks in advance.

Johan

Re: FSK demodulation using ddc

Andy_Hinde — Thu, 28 Jul 2005 00:15:00 GMT

Hi Johan,
You can program the PXI-5660 to acquire continuous, gap-free data, as illustrated by the NI-RFSA 1.5 shipping example "ni5660 Fetch IQ Data.VI". This example acquires continuous IQ data. I have modified this example to add FSK demodulation to it to accomplish continuous FSK demodulation.

Regards,
Andy Hinde
National Instruments

Re: FSK demodulation using ddc

Jdttang — Thu, 28 Jul 2005 07:02:45 GMT

Thanks a lot for your fast response! We'll explore it right away and

provide some feedback.

Kind regards

Johan van der Tang

Eindhoven University of Technology

Re: FSK demodulation using ddc

Jdttang — Tue, 16 Aug 2005 09:18:21 GMT

Hi Andy,

It took some time for we could take a look at the example, as

we were first measuring chips.

As it appears , we have a PXI5600 and not a PXI5660. Is

it possible for you to point out the main differences or

better, send an example for real-time FSK demodulation

based on the PXI5600 ?

Thanks for your time in advance.

Johan van der Tang

Re: FSK demodulation using ddc

Andy_Hinde — Thu, 18 Aug 2005 18:57:34 GMT

Hello Johan,
The difference between a 5660 and 5600 is the 5600 is the RF downconverter module, and the 5660 is the pair of modules containing both the downconverter (5600) as well as the IF digitizer (the PXI-5620).

So, the 5600 is essentially a signal conditioner that (a) does frequency downconversion and (b) applies attenuation and gain and the digitizer module does all the data acquisition and transfer. It is not possible for me to send you an FSK example using just the 5600 since the 5600 does no data acquisition.

Thanks,
Andy

Re: FSK demodulation using ddc

Jdttang — Thu, 18 Aug 2005 19:49:20 GMT

Hi Andy,

Thank you for your message. Indeed, my message was incomplete. We have a
5600 plus PXI-5620 (digitizer). I interpreted a question of my PhD student to
hastely. If the combination is identical to the PXI-5660 (the bundle), than the
example should work fine for us, and we need to study your example better.
My student mentioned that the example was for the PXI-5660 and not for the
PXI-5600, just before he left on holiday, and that's what triggered my question.
Next time we take a closer look to the web-site first! When he's back we
dive into the example.

Thanks,

Johan

Re: FSK demodulation using ddc

Andy_Hinde — Thu, 18 Aug 2005 19:55:46 GMT

Hello Johan,
I apologize for the confusion. The PXI-5660 RF Vector Signal Analyzer refers to the kit available from NI that contains (1) the PXI-5600 module, (2) the PXI-5620 digitizer, (3) cables for interconnecting the two modules and (4) the Spectral Measurements Toolkit software + drivers. You should be able to use the example - just look in Measurement and Automation Explorer for the device numbers (of the 5600 and 5620) and enter these into the front panel in the appropriate place!

Thanks,
Andy

Re: FSK demodulation using ddc

Jdttang — Thu, 18 Aug 2005 20:26:56 GMT

Hi Andy,

No apology needed !; We were confusing our self

Thanks for the additional clarification!

Cheers,

Johan

Re: FSK demodulation using ddc

Jdttang — Fri, 26 Aug 2005 21:33:51 GMT

Hi Andy,

We looked into the example further and in the beginning we were missing a number of VI's (ni5660 initialize, ni5669 fetch IQ, etc). We solved that by upgrading our RFSA (and scope) driver to 1.5 (and 2.8), respectively. What is keeping us from running your example is one missing VI, called MT generate systems parameters (might be FSK in
there, you will know). We traced it back to modulation tool kit 3.0. We are using modulation tool kit 2.0. Is there a different source for this, or any way to use your example
with modulation tool kit 2.0?

Thanks for your time, indeed.

Kind Regards,

Johan

Re: FSK demodulation using ddc

Andy_Hinde — Fri, 26 Aug 2005 21:49:20 GMT

Hi Johan,
In Modulation Tooklit 2.0, there were separate VIs used for generating system parameters for each of the supported modulation types (Generate FSK System Parameters.vi, Generate QAM System Parameters.vi, etc...). In MT 3.0, this was changed to a single polymorphic LabVIEW VI, so you drop down one instance of Generate System Parameters and then select which type on the block diagram.

So, all you have to do to make this work in MT 2.0 is replace the missing subVI with MT Generate FSK System Parameters.vi from the Modulation Toolkit pallette.

I went ahead and installed 2.0 and did this in the attached (modified) example.

Thanks,
Andy

Re: FSK demodulation using ddc

Jdttang — Mon, 29 Aug 2005 09:08:53 GMT

Great! Thanks a million.

Johan