# Inconsistant Gain in X310

**URL:** <https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174>\
**Category:** GNU Radio\
**Created:** [November 21, 2014, 4:19pm UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174 "2014-11-21T16:19:31Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [November 21, 2014, 4:19pm UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/1 "2014-11-21T16:19:31Z")

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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

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<div class="post-metadata">

**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 21, 2014, 7:16pm UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/2 "2014-11-21T19:16:40Z")

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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-in-X310-tp51379p51381.html](http://gnuradio.4.n7.nabble.com/Inconsistant-Gain-in-X310-tp51379p51381.html)  
Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).

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**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 22, 2014, 1:37am UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/3 "2014-11-22T01:37:19Z")

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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 \<

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**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 22, 2014, 1:33am UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/4 "2014-11-22T01:33:42Z")

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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\_1multi\_\_usrp.html#a7beb49c1a04a81b3e7569db482453746](http://files.ettus.com/manual/classuhd_1_1usrp_1_1multi__usrp.html#a7beb49c1a04a81b3e7569db482453746)

Cheers,  
Ben

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**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 24, 2014, 4:28pm UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/5 "2014-11-24T16:28:32Z")

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**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 22, 2014, 2:26am UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/6 "2014-11-22T02:26:49Z")

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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](http://www.sbrac.org/files/test_x310_basicrx.grc)

Does this show the same problem?

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**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 24, 2014, 10:59pm UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/7 "2014-11-24T22:59:16Z")

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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](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.

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**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 25, 2014, 4:05pm UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/8 "2014-11-25T16:05:35Z")

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**Author:** ![DaigleS\_AndrewS10](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ed655f/32.png) [@DaigleS\_AndrewS10](https://www.ruby-forum.com/u/DaigleS_AndrewS10)\
**Post date:** [November 29, 2015, 6:53pm UTC](https://www.ruby-forum.com/t/inconsistant-gain-in-x310/233174/9 "2015-11-29T18:53:34Z")

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Hello,

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

Please Help.