USRP2900 - PLL - Switch "REF-IN" vs. "Internal Oscillator"

[Thierry.LE_GALL]

Hi,

I'm working with the USRP2900 and LabVIEW Communications System Design Suite.
I'm trying to control the RX frequency of the mixer using the REF IN input
connected to an external RF source. I see no change of the frequency of
the mixer in the USRP2900. Is there something to do on the HW of the USRP
or in the SW in  LabVIEW Communications System  to take the control of the
PLL of the USRP2900 using the REF IN connector connected to an external source
RF?

Regards,

[caillotantoine]

Hello,

You can use the niUSRP Property Node. Select the option Timebase Clock Source in Clocking and Synchronization menu. After auto-generating the constant as input, select RefIn.

Regards,

Antoine

[Thierry.LE_GALL]

Hi Antoine,

Thanks for your answer, but the option Timebase Clock Source is for ppsIn source (time based synchro) for the RefIn source (frequency based syncro), each of them can be used to  control the PLL. Indeed, the niUSRP Property Node is to use and then the option Reference Frequency Source has to be selected to get RefIn constant as input. Doing so, the PLL still doesn't work properly (PLL doesn't lock in the allocated time).

Kind Regard,

[caillotantoine]

Hello,

How about the same manipulation with Reference Frequency Source instead of Timebase Clock Source?

Best regards,

Antoine

[Thierry.LE_GALL]

Hi Antoine,

With Reference Frequency Source, an error message occurs : "Error - 1074118625" with a possible reason "The reference clock PLL did not lock within the allotated time", see attached snashot (*.png). The external RefIn source is a waveform generator R&S at 150MHz with a level equal to 10.0dBm, the signal waveform is a sinusoïd, the external source is connected to the RefIn input of the USRP2900 (max level 15dBm).

Regards,

[caillotantoine]

Hello,

What release of LabView Communication are you using? I found on this forum that explains that there could be a bug depending the release you are using :

http://forums.ni.com/t5/LabVIEW/USRP-Rx-PLL-Not-Locked/m-p/3587493

Ragards,

[Thierry.LE_GALL]

Hi Antoine,

I'm using LabVIEW Communications System Design Suite 2.0, build number : 4.5.2.51305.

It seems that he installation of the drivers version 16.1 + computer reboot has no effect on the issue with the HW PLL when using the RefIn input of USRP2900.

Regards, 

[caillotantoine]

Hello,

Can you try different frequencies (such as 10MHz) and power ?

Regards,

[muffin.vi]

Hi Thierry.LE_GALL,

To be clear, the REF IN port is not an LO input port. The REF IN port is for an external 10 MHz reference clock. This reference clock is used to drive a LO synthesizer that creates the actual LO. So, in other words, changing the frequency of the REF IN is not going to change the mixer frequency. The mixer frequency must be configured in SW. 

[Thierry.LE_GALL]

Hi "Muffin" & Antoine,

Thanks for your answers. Indeed 10MHz frequency allows the PLL to be locked. This solves the problem (see the snapshots in the attachment).

Regards,