RFSG Spurs on Carrier

[YuYiming]

Hi:

I am using PXI-5673 to do streaming and find spurs on the carrier frequency.

I use RFSG Arbitrary Waveform Streaming.vi and set all the streaming data equals 0. When I connect this signal to PXI-5661, I find there is a spurs about 30 dB over the noise floor. 

If I use RFSG Write Waveform From File.vi and set all data to be 0, there is no spurs.

Is there any difference between the two vis ?

[mbb25]

"30 dB over the noise floor" (of the analyzer).  Can you indicate the actual level in dBm instead?  This analyzer noise floor varies with the rbw and reference level.

Also indicate the configured power level.  Some carrier leakage is expected.  The PXIe-5673 specs an LO leakage of no more than 44 dBc below 5.5 GHz (page 19).  So if you are configuring a peak power level of 0 dBm (same as 0 dBm average power for a single tone), if the carrier leakage is -44 dBm or lower than this is expected.

[mbb25]

Also, I would expect to see the same leakage using the two VIs (assuming you have the same power level configured on both).  I notice that default power level is different in the two VIs:

• RFSG Arbitrary Waveform Streaming.vi defaults to 0 dBm (peak power)
• RFSG Write Waveform From File.vi defaults to -20 dBm (peak power)

If you are using the VI defaults, I'd expect the leakage to be 20 dB better in the latter VI. This is because the carrier leakage primarily comes from the modulator, so as you apply more attenuation both the signal and the carrier leakage are attenuated.  There is also some leakage that is due to limited isolation between the LO In and RF Out ports on the 5611 ("Local Oscillator Feedthrough" in the specs).  This component only matters when you are trying to generate low power signals.

[ChenXin1113]

From the definition of the two VIs,

RFSG Arbitrary Waveform Streaming.vi:

This example demonstrates how to read Chirp signal data in chunks from a file and then use streaming capabilities to generate it. 

RFSG Write Waveform From File.vi:

This example demonstrates how to read Chirp signal data in chunks from a file and then generate it using the the Arbitrary Waveform capabilities of NI-RFSG.