Forum: GNU Radio Inconsistant Gain in X310

Announcement (2017-05-07): www.ruby-forum.com is now read-only since I unfortunately do not have the time to support and maintain the forum any more. Please see rubyonrails.org/community and ruby-lang.org/en/community for other Rails- und Ruby-related community platforms.
F6fd81869f458e70c7959517636cc27f?d=identicon&s=25 Daigle, Andrew - 1008 - MITLL (Guest)
on 2014-11-21 16:19
(Received via mailing list)
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
57b3ceb0abd052fcadd9494ea5a030de?d=identicon&s=25 madengr (Guest)
on 2014-11-21 19:16
(Received via mailing list)
Might want to post this over on the Ettus list, as I am having issue
with the
X310 and LFRX and have a few threads on there with examples of
diagnosing
it.  The DC compensation seems to be always on (bad since the LRFX is DC
coupled), and the digital gain setting seems broke.  These may be
related to
the motherboard  not ID'ing the daughter board correctly since things
work
fine on the N210.   The DC compensation should not be an issue for your
BasicRX, but you may want to ensure the digital gain is set to zero, or
tweak it and see if it shows glitches in the time domain.  I'm wondering
now
if it's just an issue on interface B since that's also what I have my
LFRX
on; I need to move it to A and try it again.

Thanks,
Lou



Daigle, Andrew - 1008 - MITLL wrote
> peak of -52 dB). This is consistent all the way up to -20 dBm (I didn't
> 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





--
View this message in context:
http://gnuradio.4.n7.nabble.com/Inconsistant-Gain-...
Sent from the GnuRadio mailing list archive at Nabble.com.
3e80620fe492d92901b7a29b28655d63?d=identicon&s=25 Ben Hilburn (Guest)
on 2014-11-22 01:33
(Received via mailing list)
Hi Lou -

By default, the RX DC offset is enabled. You can disable it with a quick
multi_usrp call:

http://files.ettus.com/manual/classuhd_1_1usrp_1_1...

Cheers,
Ben
3e80620fe492d92901b7a29b28655d63?d=identicon&s=25 Ben Hilburn (Guest)
on 2014-11-22 01:37
(Received via mailing list)
Hi Andrew -

What you describe is very strange. There is nothing in the USRP that
changes dynamically based on the input power level (there isn't even
AGC).
The only thing I can think of is that somehow the built-in DC offset
calibration is going haywire. Are you setting the center frequency
directly
to the frequency of your input signal? If you tune with an LO offset, do
you see the same behavior?

Another question: what is your signal source? Can you lock the USRP and
your signal source to the same reference, and then tune such that your
input signal is directly "over an FFT bin"? Do you still see different
behavior between the two channels?

Also, the decimation is done in the FPGA, and must be the same for each
channel.

Cheers,
Ben

On Fri, Nov 21, 2014 at 7:17 AM, Daigle, Andrew - 1008 - MITLL <
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2014-11-22 02:26
(Received via mailing list)
On 11/21/2014 10:17 AM, Daigle, Andrew - 1008 - MITLL wrote:
> increases accordingly (i/e for a -40 dBm CW tone I see a floor of
> 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?
F6fd81869f458e70c7959517636cc27f?d=identicon&s=25 Daigle, Andrew - 1008 - MITLL (Guest)
on 2014-11-24 16:28
(Received via mailing list)
Attachment: image001.jpg (20 KB)
_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2014-11-24 22:59
(Received via mailing list)
On 11/24/2014 10:26 AM, Daigle, Andrew - 1008 - MITLL wrote:
> success with that either (outside of removing the small peak at DC). I
> though leakage occurs between the main sinusoidal wave and this
> secondary carrier signal.
>
> Thoughts? Thanks for taking the time to look at this.
>
> -Andrew
>
Andrew:

What does the following test flow-graph yield?   With the same signal
input to both sides (via a splitter):

http://www.sbrac.org/files/test_x310_basicrx.grc

If you're injecting a -50dBm test tone at 50.1MHz, you should see it at
100kHz in the FFT display of each half, and within 1dB of each other.
F6fd81869f458e70c7959517636cc27f?d=identicon&s=25 Daigle, Andrew - 1008 - MITLL (Guest)
on 2014-11-25 16:05
(Received via mailing list)
Attachment: image005.jpg (20 KB)
Attachment: image006.jpg (20 KB)
Attachment: image007.jpg (20 KB)
_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Ac9840bd7341ca9d24c5d0f2f7e60a7b?d=identicon&s=25 Yamith Becerra (yamith_b)
on 2015-11-29 18:53
Hello,

I have the USRP X310 and GPSDO (OXCO) Module.
Which UHD version installed to operate this USRP and the module?

Please Help.
This topic is locked and can not be replied to.