USRP 2921 ADC/DAC Voltage Reference

[hkhalili]

In this document:

gnuradio.org/redmine/attachments/129/USRP_Documentation.pdf

It says that the the full range of the ADCs is 2Vpp, and of the DACs, it's 1Vpp. Is this accurate for the NI USRPs, specifically USRP 2921?

Many thanks

[CharlotteN]

Hi Hkhalili, 

What is it that you're trying to do with the USRP? In the NI USRP 2921 the ADC and DAC have ranges greater than those you have stated in your post. 

Hope this helps, 

Charlotte

[hkhalili]

Hi Charlotte,

I am trying to characterise the front-end (gain). I am inputting a signal using a signal generator and it would be nice if I could assign units (dBm) to the values I read from the USRPs instead of them being arbitrary between -1 and 1.

Many thanks,

Hassan

[CharlotteN]

Hi Hassan, 

So you want to know the voltage ranges to perform that conversion from arbitary units to dBm?

Charlotte

[hkhalili]

Hi Charlotte,

That's exactly right, if possible.

Thank you

[ErikL]

It does not really make sense to work in Vp-p for rf devices. You would want to work in dBm and make sure you are matched with 50 ohm impedance. Input values from software should not exceed +/- 0.7 for each Iand Q so the complex magnitude does not exceed 1. The spec sheet for each usrp gives the maximum input range. The .chm help file that installs with the hardware gives the hardware block diagram. Amplification in the device make the maximum input power around 0 dBm for most USRP models. Also the devices are not calibrated and measurements void vary by as much as 10dBm based on temperature, time, and frequency. This is not critical in a communications system applications because the USRP has such a wide dynamic range.

[ErikL]

Spec Sheet: http://www.ni.com/pdf/manuals/375839a.pdf

[hkhalili]

Hi Erik,

Are there specs for mapping those I/Q values to dBm values?

Hassan