[USRP-users] Daughter board with a log response
vsandilya at gmail.com
Fri Apr 10 16:17:47 EDT 2015
We are feeding a pulse modulated signal at 1090 MHz to the input of the
N200 and looking at the output using Gnuradio companion. The GRC flowgraph
is really simple and it contains a USRP source, few throttle blocks, a
complex to magnitude block (which is essentially doing sqrt(I*I + Q*Q)) and
looking at the output voltage using a scope sink. We start with an input
power of -80 dbm and increase it in steps of 5 and observe the output
voltage (in mv). We take these values of input power vs output voltage and
plot it in Excel. I think the receiver was saturating around -30 dbm when
the observed output voltage was around 1340mv.
On Fri, Apr 10, 2015 at 1:12 PM, Marcus D. Leech via USRP-users <
usrp-users at lists.ettus.com> wrote:
> 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 listUSRP-users at lists.ettus.comhttp://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.
> USRP-users mailing list
> USRP-users at lists.ettus.com
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the USRP-users