[USRP-users] Not getting white noise in a USRP N210

Harold Daniel Moreno Urbina haroldmk at gmail.com
Thu Sep 4 17:02:53 EDT 2014


Sure Marcus,

----------------------------------------------------
uhd_fft.grc
----------------------------------------------------

center frequency 2.45 GHz: *http://imgur.com/mmsdO0v
<http://imgur.com/mmsdO0v>*

center frequency 2.42 GHz: *http://imgur.com/K526vsc
<http://imgur.com/K526vsc>*

----------------------------------------------------
Custom USPR2FFT
----------------------------------------------------

center frequency 2.45 GHz: *http://imgur.com/3Ukz1F8
<http://imgur.com/3Ukz1F8>*

center frequency 1.80 GHz: *http://imgur.com/CkZsFyN
<http://imgur.com/CkZsFyN>*

center frequency 900 MHz: *http://imgur.com/MfVe34m
<http://imgur.com/MfVe34m>*

center frequency 300 MHz (out of SBX used operational band):
*http://imgur.com/zSlv6PD
<http://imgur.com/zSlv6PD>*


----------------------------------------------------
Tried with other frequencies and sample rate
I looked to have a center frequency not a factor
of sample rate
----------------------------------------------------

Center freqency 452 MHz, Sample Rate 9 MSps: http://imgur.com/oLgXmqN

Center freqency 2759 MHz, Sample Rate 9 MSps: http://imgur.com/edysiBb


----------------------------------------------------
I used a second USRP N210
----------------------------------------------------

Center freqency 2759 MHz, Sample Rate 9 MSps: http://imgur.com/pwFFCPB

Center freqency 2760 MHz, Sample Rate 9 MSps: http://imgur.com/NrBbugz

Center freqency 2760 MHz, Sample Rate 10 MSps: http://imgur.com/2NTmi2f

Center freqency 2760 MHz, Sample Rate 10 MSps: http://imgur.com/CZ4oHOF


I can see that when I use 10 MSps the signals is much more flat than the
signals captured with 9 or 11 MSps.



2014-09-04 14:33 GMT-06:00 Marcus Müller <usrp-users at lists.ettus.com>:

>  About the pictures: Would you mind uploading them somewhere else? It
> really takes ages for me to see a single one, and it blocks parallely
> waiting for multiples, so I must admit I only saw the first two before I
> gave up. Maybe imgur.com?
>
> Greetings,
> Marcus
>
> On 04.09.2014 22:12, Ian Buckley via USRP-users wrote:
>
> Good point, I answered that very quickly without looking at the downloads. Do you understand Marcus's point about direct conversion architectures? It was perhaps more appropriate.
>
>
>
> On Sep 4, 2014, at 1:04 PM, Harold Daniel Moreno Urbina <haroldmk at gmail.com> <haroldmk at gmail.com> wrote:
>
>
>  But neither 2.45 GHz nor 2.42 GHz are factor of 100 MHz. The other frequencies used are (1.8 GHz, 900 and 300 MHz).
>
>
> 2014-09-04 13:53 GMT-06:00 Ian Buckley <ianb at ionconcepts.com> <ianb at ionconcepts.com>:
> Very likely it's a harmonic of the 100MHz clock used extensively in the N210.
> Try tuning to a frequency thats not a factor of 100MHz and see if it is still there.
>
> On Sep 4, 2014, at 12:24 PM, Harold Daniel Moreno Urbina via USRP-users <usrp-users at lists.ettus.com> <usrp-users at lists.ettus.com> wrote:
>
>
>  Hello,
>
> When using USRP N210 without an antenna I would expect to receive white noise, right?. But consistently I am getting signal at center frequency well over 20 dB compared to other frequencies and 30 or dB over the signals near the edge.
>
> Anyone knows what is happening here? Is something wrong in the USRP or in GNU Radio? or me? Thanks.
>
>
> I am using USRP N210, GNU Radio 3.7.2.1 (version of last friday) over Ubuntu 14.04.
>
> I uploaded some screenshots of the FFT of the received signal, always 10Msps and getting about 5 minutes of signals. I used the example included in GNU Radio uhd_fft.grc and a custom flowgraph icluding only a USRP source and a FFT sink.
>
> ----------------------------------------------------
> uhd_fft.grc
> ----------------------------------------------------
>
> center frequency 2.45 GHz: https://mega.co.nz/#!WFE3UTRZ!AO04usGbl9TBa5-mCUPz7FYW2IabY5nbo5zZqSWwaM4
>
> center frequency 2.42 GHz: https://mega.co.nz/#!Hc0UzBJA!fSfgScdXPJ_phKdIWUKcNseonlKQt3m64yvYMR0bDhs
>
> ----------------------------------------------------
> Custom USPR2FFT
> ----------------------------------------------------
>
> center frequency 2.45 GHz: https://mega.co.nz/#!Hd9RyApS!FzsY5yxr5e6dJaAAO7Ww2O4BFefyCk6MDPN6ffcOs_g
>
> center frequency 1.80 GHz: https://mega.co.nz/#!LQcTkDjb!NQ7rIe1PDgRFCp547_U3mhxxxzsvQilPV-esTo7nHa4
>
> center frequency 900 MHz: https://mega.co.nz/#!eZ1TFbSY!nkt-n1mlC54aFfDwvqoJIJd7-a7gMB2GBLLhyclxxcs
>
> center frequency 300 MHz (out of SBX used operational band): https://mega.co.nz/#!mJ8EESwR!lI_0r4RvvTncxwwMnpEVAvrwsVhcHzLX7H6C7TA4Cj0
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