Re: [Discuss-gnuradio] Inconsistant Gain in X310

[madengr]

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
> 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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