[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:
> 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.
> John Keller
> USRP-users mailing list
> USRP-users at 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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