RF Measurement Devices

[Betty Boop]

Hello.

I would just like to ask how do I remove the frequency offset if I use an external RF signal generator (instead of the NI PXIe-5652 RF Signal Generator module). I understand that in the case of using the NI to generate RF signal, frequency offset is removed by setting the same reference clock source for the transmitter and receiver (setting the reference clock source to PXI_CLK in the front panel of both generation VI and acquistion VI).

Thank you very much.

[Andy_Hinde]

Hi Betty,

The answer to your question is to have both your acquisition devices and your signal generator use the same reference clock. There is a BNC terminal on the back of the PXI chassis which provides access to the PXI backplane clock (10 MHz OUT), as well as a terminal to import a 10 MHz signal into the PXI chassis as the new backplane clock (BNC IN).

You can either lock the external sig gen to the PXI chassis or you can lock the PXI chassis to the external sig gen. In general it is preferable to use the 10 MHz clock that has better specs as the master ref clock

Regards,

Andy Hinde

RF Systems Engineer

National Instruments

[Betty Boop]

Hello, Sir!

In that kind of setting, what master reference clock source should I set in the front panel? I tried both the onboard and RefIn and I got  some errors (see attachments). And do I still have other adjustments/settings to make?

Thank you.

[Andy_Hinde]

Hi Betty,

Are you using the sig gen as the master ref clock source, or the PXI chassis as the master ref clock source?

Regards,

Andy Hinde

RF Systems Engineer

National Instruments

[Betty Boop]

I connected the 10MHz REF OUT of the PXI chassis to the 10MHz REF IN of the sig gen, so I'm using the PXI chassis as the master reference clock source.

Thank you.

[Andy_Hinde · Accepted solution]

Hi Betty,

In this case, no changes are needed, as the NI modules are still using the PXI backplane clock as the ref clock source. If you are still experiencing a frequency offset, you probably need to configure the sig gen to lock to an external ref clock source. Usually, just making the signal connection is not enough - you have to also tell the sig gen to use the signal connected at its ref clock input terminal.

If you were using the sig gen as the master ref clock source, simply connecting the 10 MHz OUT of the sig gen to the BNC 10 MHz IN on the back of the PXI chassis replaces the native PXI chassis backplane clock with the newly connected one, and the analyzers are still using the PXI backplane clock as the ref clock source (no changes to SW settings).

Regards,

Andy Hinde

RF Systems Engineer

National Instruments

[Betty Boop]

Hello, Sir Andy!

You're so brilliant as always.

Thank you very much for all the help! God Bless!