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Real-time streaming of IQ data

Question asked by Michael_Betz on Dec 15, 2011
Latest reply on Dec 20, 2011 by tabbott

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Dear Agilent support,

we have an N9010A EXA Signal Analyzer with the VSA software.

What i would like to do is to record a very long time trace (several hours) to harddisk for offline analysis.

Ideally, i was thinking about a small C-application, remote controlling the analyzer over some LAN based protocol (e.g., VISA).

I found some examples, how to get single time traces with IQ data (up to the length of the internal buffer of ~ 4 MSamples). So if put the acquire command in a loop, i'll get continuous data.

My question is, can I acquire a realtime trace without gaps this way? This would be possible if there is some kind of double buffering implemented in hardware. Then I could read out one buffer while the measurement continues and fills the second buffer.

I speculate that this should be possible because the VSA software is able to do "real-time" measurements as well.

Thanks for any hints on this subject.

Best wishes
Michael

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Michael_Betz Dec 15, 2011 9:51 AM

Update:

I did a small experiment, fetching the IQ data over Telnet (SCPI). The transmission is way too slow for my application, even when binary transfer is turned on.

So now i'm wondering, how does the VSA application communicate with the spectrum analyzer?
It has a pretty good performance, showing the 4 MSample spectrum in just a few seconds.

Can i use the same interface to access the IQ data with a custom application?

Cheers,
Michael

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Michael_Betz Dec 16, 2011 7:58 AM

Update2:

This time I used the macro function in the VSA-application. The macro waits until a time-trace is acquired and then saves it to disk as a MATLAB file. This is repeated in a loop 5 times. The performance is good as saving a trace to disk is rather fast.

Unfortunately, if I look at the data in MATLAB and concatenate the slices, I can see that the data is not seamless.

Now i found in the VSA help files (Topic: Overlap), that a special "Real time measurement" needs to be started. It says, then its possible to "Real-time average" many spectras, while there will be no gap in the acquisition of the time trace.

Ho is it possible to use this real-time function?

Cheers
Michael

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tabbott

Dec 20, 2011 11:24 AM

Hi Michael -

A recording from the 89600 VSA software provides gap-free data capture from the EXA, but the maximum length the VSA software can record is limited by the amount of memory in your hardware. The entire recording gets written to the hardware memory and then transferred out to the software. Writing a program like you describe would result in gaps between acquisitions when the data is being transferred out of the hardware memory.

There is a streaming solution that uses the EXA (or MXA/PXA with the B40 Digital IF installed) as a front-end to provide real-time streaming to a RAID by a company called X-COM. They provide software they have written to control the hardware and stream the data out of the LVDS port. One of the nice things about X-COM’s solution is that they can play back the recording and extract portions of it into our 89600 VSA Software for further analysis. This software package from X-COM is called Spectro-X.

This is a third-party solution supported by X-COM and any specific X-COM questions can be sent directly to them. Their website is http://www.xcomsystems.com and contact information (by region) is available at http://www.xcomsystems.com/info/.

Regards -

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Michael_Betz Dec 15, 2011 9:51 AM
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Update:

I did a small experiment, fetching the IQ data over Telnet (SCPI). The transmission is way too slow for my application, even when binary transfer is turned on.

So now i'm wondering, how does the VSA application communicate with the spectrum analyzer?
It has a pretty good performance, showing the 4 MSample spectrum in just a few seconds.

Can i use the same interface to access the IQ data with a custom application?

Cheers,
Michael
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Michael_Betz Dec 16, 2011 7:58 AM
Mark Correct
Correct Answer
Update2:

This time I used the macro function in the VSA-application. The macro waits until a time-trace is acquired and then saves it to disk as a MATLAB file. This is repeated in a loop 5 times. The performance is good as saving a trace to disk is rather fast.

Unfortunately, if I look at the data in MATLAB and concatenate the slices, I can see that the data is not seamless.

Now i found in the VSA help files (Topic: Overlap), that a special "Real time measurement" needs to be started. It says, then its possible to "Real-time average" many spectras, while there will be no gap in the acquisition of the time trace.

Ho is it possible to use this real-time function?

Cheers
Michael
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tabbott Dec 20, 2011 11:24 AM
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Hi Michael -

A recording from the 89600 VSA software provides gap-free data capture from the EXA, but the maximum length the VSA software can record is limited by the amount of memory in your hardware. The entire recording gets written to the hardware memory and then transferred out to the software. Writing a program like you describe would result in gaps between acquisitions when the data is being transferred out of the hardware memory.

There is a streaming solution that uses the EXA (or MXA/PXA with the B40 Digital IF installed) as a front-end to provide real-time streaming to a RAID by a company called X-COM. They provide software they have written to control the hardware and stream the data out of the LVDS port. One of the nice things about X-COM’s solution is that they can play back the recording and extract portions of it into our 89600 VSA Software for further analysis. This software package from X-COM is called Spectro-X.

This is a third-party solution supported by X-COM and any specific X-COM questions can be sent directly to them. Their website is http://www.xcomsystems.com and contact information (by region) is available at http://www.xcomsystems.com/info/.

Regards -
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