saving spectrum with 5660

[JSflow]

I need clarification on output data from 5660 to save the spectrum data.

Span:10MHz

Center: 30MHz

RBW: 1KHz

Question: Can I save this data in real-time continuously without using external disk controller card?

I am confused with the output rate, such as "Min. Sample Rate" from Digitizers.

Does the sample rate determined by Span, or is 64MS/s of 5620 applied everytime?

If it's 64MS/s no matter what, then I can't save spectrum data continously in my HDD, right?

Thanks

[Ayman K]

Hello JSflow,

The PXI-5660 is composed of an analog RF downconverter which places the downconverted RF spectrum at an IF frequency span between 5 and 25 MHz. The spectrum from 5-25 MHz is what the second module, the PXI-5620 64 MS/sec digitizer sees. The digitizer is a 14 bit device and hence takes 2 bytes per sample. Transfer rates this high cannot be sustained. However, a solution exists if signals <= 1.25 MHz in bandwidth are being analyzed. In this situation a Digital Downconverter (DDC) chip present on the PXI-5620 turns on and downconverts the IF input of the 5620 to 0 Hz and outputs baseband IQ data. This process includes digital downconversion, filtering, and finally decimation, with the decimation being key to sustained continuous acquisition. The sampling rate drops from 64 MS/sec to 2 MS/sec for spans <= 1.25 MHz and goes below 2 MS/sec depending on how narrow your configured bandwidth is. The main point though is that when the DDC is on, continuous data transfer is possible and the space required is easily calculated based on sampling rate and hard disk size. The DDC hardware has eight discrete bandwidth settings. You can get a list of these discrete settings and  the associated decimation and sample rate at the following path in the NI RFSA Help  (NI RF Signal Analyzers Help -> Fundamentals -> Small Span signals and Small Rates). Please let me know if you have further questions.

Ayman K

[crueger]

Hi.

I want to do a continously spectrum Acquisition using the NI PXI 5661. therefor i configured the  RFSA. My Question is can i trigger the 5661 with an external or internal trigger source so that for example every 5 ms a trigger is send and a new Measurement is beeing performed, becuase now by perfoming acquisition only 1 shot is made and the application finishes.

Thanks.

Christian

[David L.]

Hi Christian,

Welcome to the NI forums! I believe the easiest way to perform the functionality you are looking for is to do a finite task and then re-start the task after every acquisition. The RFSA Initiate VI will take about 2ms, so having a trigger come every 5ms should not be a problem. To implement this, put the initiate and fetch VI’s inside a while loop, therefore after every fetch, it will begin the loop over again, re-initiate the RFSA, and re-arm the trigger. If you have any problems, I would like to ask for you to post the code you are using along with screenshots for any errors.

[crueger]

Hi David.

I have done it with an internal Windows Timer at first and it runs.
Now there is a new problem: I'm in Spectrum mode and want to trigger the PXI with a Hardware Trigger. therefor i send an pulse from a function Generator to the PXI.
The Problem is that an error message pops up: This Trigger type is not supported with the spectrum mode.
My Question is can i send a hardware trigger to the PXI in Spectrum mode so that everytime a pulse is send an Acquisition is made?
For this i tried to communicate with the AUX I/O Input the PFI 0 Line but it doesn't worked. The same error message as written above.

Then i had the idea to send the trigger to the TRIG Input channel at the Digitizer but fpr this i found no help in the niRFSA Help file. How can i manage this?
I tried to do this and opened a new session to the digitizer but this doesn't work because i can only open one session on the PXI and this i have already done with the niRFSA 5661.

Do you have an idea how i can solve this problem or where to find help??

Thanks
Christian

EDIT: I forgot to say that i program with visual Studio 2005 in C#



Message Edited by crueger on 06-23-2008 07:57 AM

[crueger]

I solved the problem. Everything's ok.