[USRP-users] Daughter board with a log response

Marcus D. Leech mleech at ripnet.com
Fri Apr 10 13:12:10 EDT 2015


On 04/10/2015 12:33 PM, John Keller via USRP-users wrote:
> Hello
>     We are using a USRP N200 that has a DBSR2X daughter board. We are 
> decoding signals at 1090 MHz that have a very large dynamic range Our 
> old system used receivers that had log amps with a dynamic range of 
> over 80 db and are linear when you plot input power vs output amplitude.
>  We plotted the output of the DBSR2X using a signal generator as an 
> input source. We then plotted the input power vs output amplitude and 
> it is very non linear. Do you have a daughter board with a log 
> characteristic or could you suggest another way.
>   Thank you.
> Regards,
> John Keller
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
How are you plotting this?

The power of a signal is proportional to the square of the voltage. The 
DBSRX2 receiver should be very linear, except at the very upper end, 
perhaps.

Logarithmic amplifier chains are generally *ONLY* used in 
high-dynamic-range power detection, they aren't general-purpose RF 
subsystems.

The DBSRX2 on an N200 should have more than 80dB of dynamic range, 
depending on sample rates, and bandwidth settings of the DBSRX2 card.

The instantaneous power of a signal can be calculated using:

P = (I*I)+(Q*Q)

Square-root and average to taste.

So, what is it that you're actually measuring and plotting?  The DBSRX2 
should be quite linear over a fairly large dynamic range.



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20150410/dcfc8074/attachment-0002.html>


More information about the USRP-users mailing list