5663 data format

[Sharmi]

Hi,

I am using PXIe-5663 for my project. I had a general question on PXIe-5663.

From the signal path it seems, an incoming RF signal is down-converted to IF by 5601 and 5652 and then digitized by 5622. Labview programming can be done to read the digitized data an view its I/Q spectrum. So when I use the niRFSA Acquire Continuous IQ vi to view the I and Q channels why do I see the analog waveform? Should I not be able to see the digitized data?

Could someone please clear my confusion?

Thanks so much,

Sharmi

[Marcus_M]

Hello Sharmi,

I believe the confusion is in the purpose of the VI.  The VI that you are referring to, niRFSA Acquire Continuous IQ, is meant to simply acquire RF data and display it in an I and Q format where each value is displayed on an analog waveform graph.  If you are looking for the digitized date you need to use Modulation Toolkit.  By opening up an example from Modulation Toolkit based on the type of signal you are generating you will be able to modulated the analog data that you are seeing right now and turn it into a digitized value.  

What type of signal are you generating that is being read into your PXIe-5663?

Regards,

Marcus M

Application Engineer

National Instruments

[Sharmi]

Hi Marcus,

The data which I am trying to view in IQ format is a conttinuous RF carrier which has been modulated by respiration/breathing. I have tried Modulation toolkit as well but the analog demodulation schemes like AM, FM do not retun complex data. So I cannot view the I an Q spectrum. Thats why I am using this vi.

If I see analog data , does it mean that 5622 is not involved when I use niRFSA Acquire Continuous IQ vi? I thought Lab view reads data after it has been digitized by 5622. I want to know the signal path in 5663. 

Thanks so much,

Sharmi

[Anthony_F]

Hello Sharmi,

Can you post a screenshot of the data you are receiving?  What does your baseband signal look like?  How does this differ from what you are expecting?

You are correct, the signal is frequency shifted from the RF frequency to the IF frequency by the 5601. From there, the 5622 samples the signal and creates a digital representation of the signal. You should see the 5663 Theory of Operation for more information

The only way that the baseband signal can exist on the computer is in digital form, so I'm confused when you say you are seeing analog data.

[Sharmi]

Hi Anthony,

Please find attached the screenshots.

Pleaselet me know if you need any other information.

Thanks so much,

Sharmi

[Anthony_F]

Sharmi,

Thanks for the screen shots, however I still find a lack of information and/or direction as to what actually needs to happen to get your expected result.

Please correct me if there is any incorrect assumptions:

1. A transducer will be used to monitor breathing activity.
2. This signal will be used to modulate a carrier wave to wirelessly transmit the breathing activity.
3. This signal will be received and demodulated by the PXIe-5663 RFSA

What type of modulation are you using to modulate the carrier? (AM, FM, QAM, FSK, PSK).  To de/modulate the signal, Modulation Toolkit has most of the common types of de/modulation functions already written so you do not need to lock on to the carrier signal and pick the correct samples.  I'm also confused why you would need "complex data" if you have a single signal as your message. Can you elaborate on some of your requirements?

I would say that if the modulation takes place on a third party upconversion system with just a single message signal, then a simple analog modulation scheme such as AM or FM would work great. Alternatively, if your data is being digitized on the chassis then you open up some more options such as PSK or FSK digital transmissions.

[Sharmi]

Hi Anthony,

Your assumptions are correct. However, I am not modulating the carrier as it should be modulated by breathing.

• I only need to send the RF carrier which I am using RFSG Single Tone Generation vi.
• I was using demolulation schemes initially but as suggested by one of NI application engineers(Reference#7363170) I used RFSA Acquire Continuous Signal vi. 

•  Since PXI system is designed with a heterodyne digital quadrature demodulation architecture we want to view both the I and Q  components of the acuired signal in time domain. Also, since I  was able to see the modulted data I with this vi, I continued using this vi. My only curiosity  was when  I acquie the data, why is it in alanog form and not digital data.

  Please let me know if you need any other information.

  Thanks so much,

  Sharmi