[USRP-users] TwinRx transfert function

Olivier Ravard olivier.ravard at novagrid.com
Wed Nov 6 13:09:24 EST 2019


Le 06/11/2019 à 18:49, Marcus D. Leech a écrit :
> 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.
The sample rate is of course 100 Msps... I just display only the 80 MHz usefull bandwidth.
>
>
>>
>> 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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