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

Marcus D. Leech mleech at ripnet.com
Thu Sep 4 22:23:50 EDT 2014


On 09/04/2014 04:33 PM, Marcus Müller via USRP-users wrote:
> 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
Also, if the input isn't terminated, it's not getting precisely thermal 
noise.  An open connector is like a little tiny, inefficient antenna, so 
there'll
   be some lumpiness in the spectral distribution that isn't random.


> 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>  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>:
>>> 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>  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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>>
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