On 11/21/2014 10:17 AM, Daigle, Andrew - 1008 - MITLL wrote:
Hello,
I am running into a small issue with the X310 USRP. My basic setup
involves receiving from two antennas (or at this point CW tones from
signal generators) using two basic RX daughter cards.
My problem is that when I pump in a -50 dBm CW tone to channel A the
FFT plot makes sense in that it is stable with an expected value
(floor ~-117 dB and peak -62 dB). As the signal increases the peak
increases accordingly (i/e for a -40 dBm CW tone I see a floor of
~-117 dB and a peak of -52 dB). This is consistent all the way up to
-20 dBm (I didn't want to get too close to the -15 dBm limit written
on the outside of the USRP). When I move this signal into channel B
its FFT mirrors channel A at an input of -50 dBm, but as soon the
signal is increased past -45 dBm the noise floor starts jumping from
~117 dB to ~93 dB rapidly and the peak jumps and stays stable 14 dB
higher (-38 dB vs -52 dB for the same -40 dBm). Below a -50 dBm input;
however, everything is identical between the two channels. I was
thinking maybe the decimation rate is changing on the second channel
based on the input power (but for some reason not the first). The
thing is I am using code loosely based on the rx_multi_samples example
and I don't know if there is a way to specify the decimation rate of
each of the daughter-cards as if I was using GNU radio companion (or
even if this is even the cause of my problem and I should be looking
elsewhere).
Any thoughts? Thanks!
-Andrew
Andrew:
You haven't mentioned things like center frequency and configured
sample-rate, but here's a test script--you will have to modify it to
meet your
test conditions, but it assumes a BASIC_RX in each slot on the X310,
and the basic 1GiGe interface, running at 1.0Msps.
http://www.sbrac.org/files/test_x310_basicrx.grc
Does this show the same problem?
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
_______________________________________________
Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
