11-22-2010 05:04 PM
thanks for the reply.
1. Record and Playback Reference Application v02 (lv85).zip 1091 KB has a vi called configure and record.vi this is what i was referring to.But I guess the second question is now more important for me to focus on.
2. Seems the location I pointed was wrong and the explanation u gave is helpful.
My goal is to use the IQ signal in L1 band from RFSA. this is why i was trying to use the record and playback application. But if you could mention any other example where i can have the L1 = 1.57542GHz IQ signal using NI RFSA that would be very helpful.
11-23-2010 02:03 PM
Well, if you just want to record IQ data to file then this application should work perfectly fine for 1.57542 GHz collecting. The Reference application records data as Int16 IQ interleaved data (little-endian by default I believe but I've switched it to big-endian in my usage).
It wouldn't take too long for you to modify the niRFSA Simple Record VI to suite your needs if you didn't want to use the entire Record & Playback UI. However, I think the Set RFSA Record Settings VI that pops up before recording is very useful for viewing the signal you want to collect before you actually do.
11-23-2010 03:05 PM
The problem is when i look at the spectrum of the signal given the parameters to generate L1 band signal there is only a single peak which means no indication of mudulated signal (there is a plain sinusoidal signal not mudulated and spread with code as it should be in case of L1 band signal).
Could you please explain why it is so ? is there a problem with the hardware or the software ?
11-23-2010 04:22 PM
I'm not sure why your system isn't seeing the signal since I'm not really familiar with GPS much. Also, there are many factors that could be affecting the ability of your VSA to "see" the GPS signal (i.e. weak GPS receive antenna may cause the GPS signal to be below the noise floor of the VSA or maybe the reference level/bandwidth of the VSA isn't set appropriately...idk).
I found a cool website that has a rough picture of what you should see in the signal's spectra http://eenotebook.co.uk/GPS.htm. Other than that I'm not sure I can be of much more help to you :-). Good luck though.
11-23-2010 05:04 PM
Make sure your GPS antenna has a LNA that amplifies your signal before heading to your VSA. Depending on the gain of this LNA, it would be useful to also have the PXI-5690 amplifier on front so that your GPS recording has maximum dynamic range.Take a look at this GPS receiver test application note.
Like Tim is saying, use the Set RFSA Record Settings VI to visualize your signal. Even if it looks very low its ok since GPS signal can be under the noise floor since they have extra 30 dB spreading gain.
11-23-2010 05:41 PM
thanks for the reply. Currently I don't have neither GPS antenna nor preamplifier. In my hardware setup the RFSA is connected to RFSg by simple wire.
And when I use Set RFSA Record Settings VI to visualize the signal it is the same as I check it with the RFSA soft front panel with only a singe peak on the input frequency i give.
Whay should I do ? any advice ?
11-23-2010 05:51 PM
If you are connected to the VSG, then you should be generating a signal correct? What type of signal is this? The tone is probably the LO leakage if its in the order of -70 dBm.
Can you describe your end goal? If you are trying to record GPS signals of the air, you will need a GPS antenna just like Figure 7 on the application note posed before this.
11-24-2010 11:14 AM
Thanks a lot for the reply. My main goal is to be able to receive L1 band GPS IQ signal on the RFSA and run my own processing code on it.
I dont' have ni preamplifier but I connected VSG to VSA instead of wire with active gps antennas.
how can I get GPS IQ signal on RFSA ?
11-24-2010 11:31 AM
If you need GPS L1 IQ data you have two options:
1) Simulated. Use the GPS Toolkit to create your own data. Since is software you can do the processing without hardware or you can generated into the VSG to validate it in a different receiver. No point in recording it with VSA.
2) Recorded. You need to recorded "off the air" and not from the VSG. You need an active antenna and the setup that is described on the application note. After successfully recorded the data, you can post process the IQ recorded data.