niRFSG_WriteArbWaveform with NIRFSG_ATTR_POWER_LEVEL_TYPE

[ilyak]

Hello:

I'm trying to configure PXO-5673 in streaming mode with NIRFSG_ATTR_POWER_LEVEL_TYPE set to NIRFSG_VAL_AVERAGE_POWER. The help for the niRFSG_WriteArbWaveform says:

Note  This function only supports NIRFSG_VAL_PEAK_POWER mode as specified in the NIRFSG_ATTR_POWER_LEVEL_TYPE attribute. If a waveform is downloaded using this function, NIRFSG_ATTR_POWER_LEVEL_TYPE cannot be changed to NIRFSG_VAL_AVERAGE_POWER mode without causing error in the output.

And appropriately I get this error:

Error -1074117681:This function is not supported when the Power Level Type is set to Average Power. Either change the Power Level Type to Peak Power or use a different write function.

Then the question is: which function should I use to write the waveforms?

Thanks so much,

-Ilya.

[chris_amadasun]

Hello Ilya,

The behavior you described is expected. This setting requires that the magnitude of the I/Q waveform must always be less than or equal to one. When using peak power, the power level of the RF signal matches the specified power level at moments when the magnitude of the I/Q waveform equals one.

You will need to modify your waveform so that the magnitude of your I and Q samples is less or equal to one. Use the formula provided in the NI RF Signal Generators Help under the NIRFSG_ATTR_POWER_LEVEL_TYPE.

Let me know if this helps.

Regards

[ilyak]

Hi Christian:

I understand that the error is expected and that the level should be <=1.

My question is - since the error code says that I can't use niRFSG-WriteArbWaveform with NIRFSG_ATTR_POWER_LEVEL_TYPE, what function should I use then? Or you are saying that the IQ file I'm trying to generate has data >1 and this is what is actually causing the error?

Thank you,

-Ilya.

[ilyak]

Hi Christian:

One more question: is there any document describing what parameters and commands can work with NIRFSG_VAL_AVERAGE_POWER set? I find that I have do trial and error to figure out what I can or cannot do when NIRFSG_VAL_AVERAGE_POWER is enabled. 

For example, script generation doesn't work (why? such a useful feature for short waveforms).

Thank you,

-Ilya.

[chris_amadasun]

Hi Ilya,

I'm not sure what the issue is. Are you using LabVIEW?

There is an example in Example Finder RFSG Arbitrary Waveform Streaming.vi, the example uses the niRFSG Configure Power Level Type VI to set the power level type to peak power. It then uses the niRFSG Write Arb Waveform VI to write a waveform to the the RFSG device.

This example wrongs without any issues. Can you send me the binary file (.bin) you are generating from?

[ilya_ktsn]

Hi Christian:

1. I'm not using LabVIEW. I do have it, however.
2. I have checked the example - RFSG Arbitrary Waveform Streaming.vi - and it runs fine or me also. However, it sets the power level to PEAK_POWER. The question I have is when the power is set to average.
3. From some trial and error I found that I have to use niRFSG_WriteArbWaveformComplexF64. However, the manual doesn't say anything about this requirement. So I was wondering if there are some additional limitations/conditions that must be observed when AVERAGE power is used.

-Ilya.

[chris_amadasun · Accepted solution]

Hello Ilya,

I'm sorry I misunderstood your question.

If you look through the NI RF Signal Generator Help manual under NI-RFSG C Function Reference.

Expand NI-RFSG Properties >> Generation configuration >> Configure Waveform >> niRFSG_WriteArbWaveformComplexI16

Note  This function only supports NIRFSG_VAL_PEAK_POWER mode as specified in the NIRFSG_ATTR_POWER_LEVEL_TYPE attribute. If a waveform is downloaded using this function, NIRFSG_ATTR_POWER_LEVEL_TYPE cannot be changed to NIRFSG_VAL_AVERAGE_POWER mode without causing error in the output.

The ni_RFSG_WriteArbWaveformComplexF64 on the other hand does support this power level type mode.

Dose this help?

[aki_t]

Regarding the original statement:

---

I'm trying to configure PXO-5673 in streaming mode with NIRFSG_ATTR_POWER_LEVEL_TYPE set to NIRFSG_VAL_AVERAGE_POWER.

---

Streaming and setting the power level type to average power will not work.  If we take a look at the RFSG help for the power level type, the driver in average power will "maximize[s] the dynamic range by scaling the I/Q waveform so that its peak magnitude is equal to one."  In order to do this, RFSG will need the entire waveform to analyze it properly.  Since direct download on the PXIe-5673 is always enabled, there is no way to write waveforms in chunks when the power level type is set to average power.  Peak power does not have this restriction since the user has control of the software scaling factor and therefore must be used when waveforms need to be written in chunks (i.e. streaming).