NI USRP for Precise Peak Power Measurement

[Tomi10]

Hi,

I would like to know if the USRP can measure the precise peak power of an unmodulated signal at a certain carrier frequency. In this scenario, we know our product is outputting 19dBm at the source with 60dB attenuation in the path to protect the USRP. Through an R&S spectrum analyser, we have measured a peak power of -47dBm, which is basically 19dbm-60-(path loss). Should we expect the same result on the USRP? I have come across some NI forum comments saying the USRP is not calibrated, so does this mean we need to adjust any measured peak power from the USRP to that measured on the R&S instrument?

Regards!

Tomi

[James_Battleaxe · Accepted solution]

Hi Tomi,

You are correct that the USRP is an uncalibrated instrument. What that means is that the specs we provide are typical but cannot be guaranteed. These instruments are meant to be used more for prototyping purposes rather than Verification and Validation testing. It is totally valid to compare the values you measure on the USRP against a calibrated instrument to check how close the values are. At that point, you can program in an offset to correct for any errors in measurement. 

We do also have a variety of Vector Signal Analyzers that are calibrated meaning that their specs are covered by the device warranty. If those devices are not measuring according to spec, we can re-calibrate the device or repair it in order to ensure that it is meeting the stated specs.

Let us know if you have any additional questions.

[Tomi10]

Understood, thanks James!

Is there a possibility to manually calibrate/set the reference level on the USRP? Or do you suggest simply applying an offset in, say, measurements coming out of a LabVIEW VI?

Also, is there an expected accuracy range when applying a digital correction to the reference level during manufacturing? For e.g. +- 3dB?

Tomi

[James_Battleaxe]

Hi Tomi,

The reference level on the USRP can be adjusted in software. There's a function in the NI-USRP driver that can set the reference level. In terms of accuracy, you will have to characterize the device you get. Since the device is uncalibrated, different devices will have different performance. In order to know more about the performance of your particular USRP, you'll have to characterize your particular device.