[USRP-users] UBX coherence between TX and RX

Michael R. Freedman mfreedman at ll.mit.edu
Wed Mar 27 10:41:08 EDT 2019


Any thoughts on this?


Mike


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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>>>>>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>>
>>>>
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>>>
>>>
>>>
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>>
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>>
>
>
>
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