[USRP-users] UBX coherence between TX and RX

Marcus D. Leech patchvonbraun at gmail.com
Wed Mar 27 15:42:07 EDT 2019


On 03/27/2019 03:39 PM, Michael R. Freedman via USRP-users wrote:
>
> Marcus,
>
>
> I tried a 10MHz LOOffset with no change.  I also tried it at 1155.0MHz 
> and 1160.0MHz.  At 1155 the phase rolls... at 1160 it does not.
>
>
> Mike
>
Could you give us a dump of uhd_usrp_probe for an X310 that displays 
this issue?  What version of UHD?   Also, to be clear, this is within
   a *single* X310, correct?


>
> On 03/27/2019 11:10 AM, Marcus D. Leech via USRP-users wrote:
>> On 03/27/2019 10:41 AM, Michael R. Freedman via USRP-users wrote:
>>>
>>> Any thoughts on this?
>>>
>>>
>>> Mike
>>>
>> Given that in this case, the incoming carrier will be fighting 
>> DC-offset removal rather hard, I wonder if this is a weird artifact 
>> of DC-offset
>>   removal?
>>
>> If you use offset tuning on the RX, do you still see a significant 
>> phase roll?
>>
>>
>>>
>>> On 03/25/2019 01:04 PM, Michael R. Freedman via USRP-users wrote:
>>>>
>>>> Marcus,
>>>>
>>>>    190Hz is what we calculated.  I have attached a text file with 
>>>> the data we used.  This is a single UBX40 tuned to 155MHz sampling 
>>>> at 2MHz.
>>>>
>>>>
>>>> Mike
>>>>
>>>>
>>>> On 03/25/2019 12:34 PM, Nick Foster wrote:
>>>>> Well, according to your description, you could transmit a carrier 
>>>>> from TX to RX (through an attenuator) with both sides set to the 
>>>>> same frequency. Your received signal should look like a sine wave 
>>>>> at the frequency of the offset.
>>>>>
>>>>> On Mon, Mar 25, 2019 at 9:16 AM Michael R. Freedman via USRP-users 
>>>>> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> 
>>>>> wrote:
>>>>>
>>>>>     Hello,
>>>>>
>>>>>     Do you have any suggestions as to how to measure the frequency
>>>>>     delta between the transmit channel and the receive channel?
>>>>>
>>>>>     As I sat down to do this, I realized I have no real way to do
>>>>>     that.
>>>>>
>>>>>
>>>>>     Mike
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>     On 03/24/2019 03:23 PM, Marcus D. Leech via USRP-users wrote:
>>>>>>     On 03/24/2019 02:39 PM, Freedman, Michael - 1008 - MITLL via
>>>>>>     USRP-users wrote:
>>>>>>>     It is not just a phase offset. It is a frequency offset. The phase drifts between the two. I can tolerate a phase offset at startup. A freq offset however is causing problems.
>>>>>>>
>>>>>>>     Mike
>>>>>>>
>>>>>>>     Sent from my iPhone
>>>>>>>
>>>>>>>     On Mar 24, 2019, at 4:28 AM, Marcus Müller<marcus.mueller at ettus.com>  <mailto:marcus.mueller at ettus.com>  wrote:
>>>>>>>
>>>>>>>     Can you elaborate on what "not coherent" means to you – the relative
>>>>>>>     phase should be constant after each tune, but if you don't tune
>>>>>>>     simultaneously, i.e. with timed commands, random at each tune.
>>>>>>>
>>>>>>>     Best regards,
>>>>>>>     Marcus
>>>>>>     Also, what version of UHD?  What hardware rev of UBX cards?
>>>>>>
>>>>>>
>>>>>>>     On Sat, 2019-03-23 at 17:06 -0400, Michael R. Freedman via USRP-users
>>>>>>>     wrote:
>>>>>>>>     Hello,
>>>>>>>>
>>>>>>>>
>>>>>>>>     I have an issue where I tune both the TX and RX side of a UBX40 card
>>>>>>>>     in
>>>>>>>>     an X310 to the same frequency and find that the transmitted signal
>>>>>>>>     and
>>>>>>>>     what is received are not coherent.  I am using an external 10MHz
>>>>>>>>     reference and have tried the documented suggestions.
>>>>>>>>
>>>>>>>>     at 150MHz it is coherent.
>>>>>>>>
>>>>>>>>     at 155MHz it is NOT coherent.
>>>>>>>>
>>>>>>>>
>>>>>>>>     I have tried setting the dboard_clock_rate to 20MHz.  This made the
>>>>>>>>     problem appear at 150MHz as well.  I've tried integer_n tuning.
>>>>>>>>
>>>>>>>>     I have verified that the ref_lock and lo_lock are both true.
>>>>>>>>
>>>>>>>>
>>>>>>>>     Any suggestions?
>>>>>>>>
>>>>>>>>
>>>>>>>>     Mike
>>>>>>>>
>>>>>>>>
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>>>>>>>
>>>>>>>
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>>>>>>
>>>>>>
>>>>>>
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>>>>>
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>>>>>
>>>>
>>>>
>>>>
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