how to use PXIe 5652 as external clock to the USRP

[Jay_c]

Hi,everyone,I'm new to PXI and USRP,and there are some problems I want to ask for help.

What I want to do is to synchronize 8 USRPs which are used as receivers. To make sure they have the same crystal oscillator, I want to use the PXIe 5652 as the external clock.However, what confuse me are that PXIe 5652 has 3 connector(RF out, REF in/out, REF out2), and USRP 2920 has REF in and PPS in, how to connect them? Wheather I need to connect the PPS in to achive my aim? And,if it is needed to write some labVIEW programs to make PXIe 5652 as the external clock? that's all,thank you!

[Jeff100]

Hi, I have same problem for connecting PXI-5661 to USRP2. 

how can I use TRIG port of PXI-5661. (PXI-5142 board)

[vvkakade]

Hi,

To provide a external reference frequency signal I think the following method can be used.

Use the niRFSG or niRFSA Export Signal VI to export the "Reference Clock" signal to "RefOut" or other appropriate output terminal.

Use the commit VI to commit these settings to the driver.

For ease you may use one of the existing RFSA or RFSG example VIs and add the export signal and commit VIs.

When the VI which opens a session to the RFSG or RFSA device is run the reference clock signal shall be exported to the configured terminal of the RFSA or RFSG device.

You may then connect this terminal to the Ref In terminal of your USRP device which you would have configured to use a external reference frequency source.

This method works for the VST which I use.

Thanks. 

[Jeff100]

Thanks.

As you mentioned, with this method we can feed "Ref Clock" port of USRP2 with the 10MHz reference frequency that is coming from PXI.

but actually my problem is feeding "PPS In" port of USRP2.

how we can configure PXI (PXI-5661) to generate and export clock (one pulse per second) to connect PPS port of USRP?

Or how can use PXI to trigger USRP?

[vvkakade]

Hi Jeff,

I am not sure if the PPS signal can be generated from the PXI 5661.

I dont know if you have already read this article about MIMO systems (if you are using multiple USRPs)

Also if you were able to generate a PPS signal from a PXI device you need a way to distribute

the PPS signal from a generator at appropriate power level to all the USRP devices to be synchronized (in case you have more than 2 devices).

This link will help too.

OctoClock

[Jeff100]

Thanks a lot for your prompt respond, highly appreciated.

Yes, I read MIMO guide. Actually they used Trimble Thunderbolt to generate ref In and PPS In.

Ok, let’s look in this way:

Is it possible to use PXIe-5661 to trigger USRP?

Or, can we feed “PPS In” port of USRP with trigger signal of PXIe (not like normal PPS signal, I mean a signal just change from zero to one whenever we need).

My goal is receiving with both PXIe and USRP simultaneously. I need some kind of trigger system to synchronize them, so they can start-stop to receive signal simultaneously.