What is the module at the Digitizer that will affect the processing time for the IQ Demodulation

[Ahmed.Abdulbaky]

Dears,

i have the following problem:

i need to do a spectrum detection of a signal and then do an IQ demodulation for this detected signal, all this process should be done in a 10ms can the Downconverter 5600 and the digitizer 5142(100MS/s and 64 MB onboard memory) do this process? and what is the Module at te digitizer which will affect on the Processing Time?

and if we use Two Digitizer (the same Previous type) one for IQ and the other for Spectrum, can this Decrease the processing time? 

[Paul_C.]

Hello Ahmed,

If you would like to do spectrum detection and IQ demodulation, this must be done in software.  This is hardware independant and will be dependent on the computer's operating system, CPU speed, etc.  So, there would be no difference between the two digitizer solution unless there was two computers to run each process.  Unfortunately, it would be impossible for me to gauge the speeds you will receive with your setup.  If you plan on using LabVIEW, our typical loop rates are in the milliseconds.  Depending on processor speed, it might be possible to achieve these rates.  However, on a windows machine there is no determinism with these loop rates.

I hope this information helps,

Paul C. 

[Ahmed.Abdulbaky]

Thank you,

you said that this Operation will be Hardware independent Process, so what is the benefit from the Onboard Signal processing (OSP) at the Digitizer module?

Best Regards

Ahmed Abdulbaky

[Paul_C.]

Hi Ahmed,

Let me provide some more information.  The Onboard Signal Processing (OSP) provided by the 5142 is used for something called Digital Downconversion (DDC).  This basically applies digital gain, digital offset, frequency translation, filtering, decimation, and some data processing.  This is used to protect against aliasing and speed up the downconversion process by doing such in hardware.  More information about the OSP can be found in the NI High-Speed Digitizer help file.  This can be viewed here.  Once you have opened the help file, please navigate to Devices » NI 5142 Overview » Onboard Signal Processing (OSP).   Here you will find a block diagram with more details on each of the components of the OSP block. 

Regarding your application, can you provide some more details on why you need the spectrum and demodulation information done in less than 10ms?  Perhaps there might be some other suggestions that I can make to speed up this process.  

 

Regards,

Paul C. 

Message Edited by Paul C. on 01-13-2009 02:29 PM

[Ahmed.Abdulbaky]

Dears,

I want to do an Experiment to Detect a Frequency Hopping Signal, I Will Watch the Spectrum till I a Signal wich Has Level More than a Threshold then i will go to this Frequency in the IQ mode to Take this Signal by IQ Demodulator, this Should be done at 10ms or the hopping rate is 100 hop/sec, Can you Help me in this Application.

Best Regards

Ahmed Abdulbaky 

[Paul_C.]

Hello Ahmed,

What bandwidth is the desired signal hopping within?  If the signal is within 20MHz, this might be possible.  Basically, the 5600 and 5142 together have a total bandwidth of 20MHz surrounding the center frequency.  If your signal of interest hops outside this bandwidth, this will require a retunning of the center frequency which may take longer than 10ms (could be up to 30ms with .00001% of step size accuracy).  Once the 20MHz band is captured, that signal checked for the signal of interest and can be sent to a processing loop for demodulation.  Depending on how this is coded, this might be possible in the 10ms requirement.  Atleast you could capture and store the signal in under 10ms.   I would use something called a producer / consumer architecture.  This design pattern can be found by going to File » New » VI » From Template » Frameworks » Design Patterns » Producer/Consumer Design Pattern (Data).  This passes data in a queue to the second consumer loop.

Regards,

Paul C

Applications Engineering

National Instruments

[Ahmed.Abdulbaky]

Thanks ALL,

Did you have any Example Which Explain How can I Fetch and Store a 20MHz BandWidth in IQ Mode, and if the Signal is a Frequency Hopping Signal in a 20MHz BW so How can I get the Center Frequency Which I will Set it to the IQ Fetch VI?

Best Regards

Ahmed Abdulbaky

[Paul_C.]

Hello Ahmed,

The 20MHz bandwidth is set by default.  You could use the RFSA Getting Started IQ.vi to fetch the I and Q information.  As for setting the correct center frequency, you will need to know before hand the 20MHz that you signal will frequency hop within.  For example, for a signal hoping between 100 and 120MHz you would set your center frequency to 110MHz.  If there are other signals within this bandwidth that you aren't interested in, you can filter these out in software after the acquisition.  Can you provide any more details of your application?  I might be able to provide more complete answers if I know what you are trying to accomplish.

Regards,

Paul C.

Message Edited by Paul C. on 02-02-2009 03:58 PM