[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, 

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

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.

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