[USRP-users] TwinRx transfert function

Marcus D. Leech patchvonbraun at gmail.com
Wed Nov 6 12:49:33 EST 2019


On 11/06/2019 12:28 PM, Olivier Ravard wrote:
> 1. The tune frequency is 1200 MHz in this case but we obtain same order of magnitude
> for fluctuations if another frequency is tuned (but transfert function could be different).
> Our tests includes L band acquisitions (950 - 2150 MHz).
>
> 2. The gain in this case is set in order to have 15 dB backoff (which is margin relative
> to the
> maximum ADC amplitude). In this case, we use 85dB gain because the noise generator gives
> a level around -135 dBm/Hz. But we observed the same things when we sample satellite
> signals using 65dB gain.
>
> 3. what do you mean by "overruns".
https://files.ettus.com/manual/page_general.html#general_ounotes

Also, How was this spectrum actually capture (in the software sense)?  
I'll note that 80Msps is not a valid delivered sample-rate for the
   X310 with any of the standard master clocks, so to capture 80Mhz of 
(analog) bandwidth, you'd need a 100Msps sample rate, which IS
   supported.


>
> regards,
>
> Olivier
>
> Le 06/11/2019 à 17:59, Marcus D Leech a écrit :
>> That is more passband ripple than I would expect.
>>
>> What is your tunes frequency. What gain setting? Are you getting overruns during the
>> measurement?
>>
>>
>> Sent from my iPhone
>>
>>> On Nov 6, 2019, at 6:32 AM, Olivier Ravard via USRP-users <usrp-users at lists.ettus.com>
>>> wrote:
>>>
>>> 
>>>
>>> Hello,
>>>
>>> We use X300 with 2 TwinRx boards for acquisitions in L band (UHD 3.10.3).
>>>
>>> It seems that the transfert function of the couple (X300 - TwinRx) shows strong
>>> fluctuations.
>>> To measure these fluctuations, we put a white noise generator at the input (this
>>> generator was
>>> measured before with a spectrum analyser and it show a very flat transfert function
>>> over 1 GHz)
>>> and we measure the PSD of the sampled 80MHz bw signal for the 4 inputs.
>>> https://files.ettus.com/manual/page_general.html#general_ounotes
>>> The result is shown on figures below:
>>>
>>> inputs 1 and 2 (first TwinRx):
>>>
>>> <bbhnehmblikapiem.png>
>>> <fpnpgddncnklhkma.png>
>>>
>>> inputs 3 and 4 (second TwinRx):
>>>
>>> <lfkojlkpiadfgnml.png>
>>> <bnokbonaahldkokn.png>
>>>
>>> Are these fluctuations normal ?
>>>
>>> regards,
>>>
>>> -- 
>>> Olivier
>>> _______________________________________________
>>> USRP-users mailing list
>>> USRP-users at lists.ettus.com
>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com




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