03-05-2012 10:32 AM
Hello!
This is about the Playback mode in the NI RF Phase-Coherent Multi-Channel version 1.1 software.
I would just like to ask if I’m expecting identical plots when I view real-time versus viewing a recorded file.
This is because when I playback the recorded xml file, I get plots which are different to those I see during real-time viewing.
Videos of the actual/real-time plots and the recorded plots could be viewed on the links below.
The phase offset has already been compensated for both cases.
Actual/Real-time: http://www.youtube.com/watch?v=W14RZwFR8MA&feature=youtu.be
Recorded: http://www.youtube.com/watch?v=GxI1STAPt2o&feature=youtu.be
Thank you very much! 😄
Solved! Go to Solution.
03-08-2012 04:51 PM
After some off-line troubleshooting with Betty Boop, we learned the following:
The next question is why the signal was being output at too high of a level. The software attempts to regenerate the signal at the exact same power level, minus some cable insertion loss.
The gain setting acquired and stored into the Record/Playback XML file is obtained from the NI-RFSA driver function niRFSA Get Scaling Coefficients. As a test, I compared this to the gain value contained in the wfm info output cluster of the NI-RFSA function niRFSA Fetch IQ (I16). They were different, and the gain value from niRFSA Fetch IQ (I16) was correct, and did change with a change in the analyzer reference level.
So for now, we are looking more closely at the niRFSA Get Scaling Coefficients subVI.
Regards,
Andy Hinde
RF Systems Engineering
National Instruments
03-08-2012 05:20 PM - edited 03-08-2012 05:20 PM
Betty what version of NI-RFSA do you have installed? This may be an issue (incorrect reported gain values by niRFSA Get Scaling Coefficients) that is fixed in the latest version of NI-RFSA, version 2.5.
http://joule.ni.com/nidu/cds/view/p/id/2666/lang/en
Regards,
Andy Hinde
RF Systems Engineer
National Instruments
03-09-2012 03:37 AM
Hello, Sir!
I'm using NI-RFSA 2.4.5. Do I need to uninstall this before installing the latest version?
Thank you! 🙂
03-09-2012 09:25 AM
Hi Betty,
If you update to NI-RFSA 2.5, your issue will be resolved.
You do not need to uninstall NI-RFSA 2.4.5 before installing NI-RFSA 2.5.
Regards,
Andy Hinde
RF Systems Engineer
National Instruments
03-13-2012 11:07 AM
03-13-2012 03:22 PM
Hi Betty,
I would recommend going back to the NI-RFSA 2.5 download page:
http://joule.ni.com/nidu/cds/view/p/id/2666/lang/en
and selecting option 2:
When you unzip this file, run setup.exe and see if this works.
Regards,
Andy Hinde
RF Systems Engineer
National Instruments
03-14-2012 11:46 AM
Here is a recent question from Betty Boop:
Hello, Sir Andy!
This is what I'm trying to do.
I generate CW signals and then record them for offline processing.
After which, I use the "Read PC Binary Data File and Write to Excel" VI.
From the Excel file, I need to get the I and Q data of the generated signals.
That is, I need to produce a total of 4 arrays:
For signal 1: one array for I data, one array for Q data
For signal 2: one array for I data, one array for Q data
These arrays will be used for baseband processing and would serve as input arrays to the code I made for my intended application.
The referenced example code "Read PC Binary Data File and Write to Excel" is located here:
https://decibel.ni.com/content/docs/DOC-21389
This code serves as a demonstration on how to read recorded binary data from a file and use the metadata stored in the Record XML file to scale the binary values to scaled voltage values. It then demonstrates how it is simple to then use basic LV File I/O VIs to write these values to an Excel file.
The data read from a single channel's data file is written to Excel in a column format, with the first column being the I data and the second column the Q data. The number of rows is the number of samples read from the binary file.
If you want to do this for two signals at the same time, you could modify this example code to do this, or you can simply run this example once for each data file, and then copy and paste data from each Excel file into a single Excel file.
Regards,
Andy Hinde
RF Systems Engineer
National Instruments
03-14-2012 12:09 PM
Hello, Sir Andy!
In getting the I and Q data of a generated and recorded signal, how do I know which samples to extract so that I can completely represent the signal?
For example, in the case of the periodic CW, I’m trying to find a pattern on the numbers listed in the Excel file. I’m assuming that repeated numbers on the file correspond to the repeated periods of the CW signal. And then I just need to consider one period to capture/represent the CW. Is this correct?
Attached is the Excel file.
Thank you! 😄
03-14-2012 01:38 PM
Hi Betty,
In the case of a sine wave being recorded to disk, a sine wave is represented by DC or static levels for I and Q vs time. The values themselves are in units of Volts.When you say:
in the case of the periodic CW, I’m trying to find a pattern on the numbers listed in the Excel file. I’m assuming that repeated numbers on the file correspond to the repeated periods of the CW signal. And then I just need to consider one period to capture/represent the CW.
I think you are misunderstanding what you should be expecting here. You won't be getting a sinusoidal pattern representing the values of the instantaneous voltage of a sine wave, which when graphed would look like a sine wave. Because the signal is downconverted to baseband IQ data and represented with complex values, you will get an array of I data and an array of Q data, where arctan(Q/I) is the phase of the sine wave and sqrt(I^2 + Q^2) represents the RMS amplitude (in V) of the sine wave. As stated above, you will see two DC values essentially, as shown in the attached JPEG which shows graphs of your 1000 samples of I and Q vs sample number.
Regards,
Andy Hinde
RF Systems Engineer
National Instruments