[USRP-users] How to correct for the drift in an (FMCW) Rx signal?

khalid.el-darymli khalid.el-darymli at mun.ca
Tue Dec 2 11:02:02 EST 2014


I am not sure if we are talking about the same thing. Since I need to track
the internal electronic circuit variation in temperature, which pins on the
USRP board/daughterboard are suitable for extracting information that
correlates with the temperature variation?

Thanks,
Khalid


On Tue, Dec 2, 2014 at 11:53 AM, Marcus D. Leech <mleech at ripnet.com> wrote:

>  On 12/02/2014 10:21 AM, khalid.el-darymli wrote:
>
>  Thanks for the prompt reply. I need to monitor the* internal temperature
> *(i.e., not the ambient temperature) of the N200 USRP board/ chip/etc.,
> to compensate for the temperature-based variations in the Rx FMCW chirp.
>
>  How the USB based sensor can do that?
>
>  Khalid
>
>  Plenty of room inside the enclosure, you'd have to use some mechanical
> creativity.
>
>
>
>
> On Tue, Dec 2, 2014 at 11:41 AM, Marcus D. Leech <mleech at ripnet.com>
> wrote:
>
>>  On 12/02/2014 10:06 AM, khalid.el-darymli wrote:
>>
>>   Hi Marcus,
>>
>>  Is there a temperature sensor on-board the N200 unit? If not, does it
>> support installing any such sensor?
>>
>>  Thanks.
>>
>>  No, and no.
>>
>> But there are a tonne of USB-based temperature sensors out there.  Google
>> is your friend, etc.
>>
>>
>>
>>
>>
>>  Best regards,
>> Khalid
>>
>>
>> On Fri, Nov 28, 2014 at 5:44 PM, Marcus D. Leech <mleech at ripnet.com>
>> wrote:
>>
>>>  On 11/28/2014 03:41 PM, khalid.el-darymli wrote:
>>>
>>>
>>>
>>>  Back to my original question, what should I do to correct for this?
>>>
>>>  Thanks in advance.
>>>
>>>  Best,
>>> Khalid
>>>
>>>
>>>     Khalid:
>>>
>>> Thanks very much for the very-extensive data.  My main concern, as one
>>> of the Ettus support team, was that there was something wrong with
>>>   the hardware, but the magnitude of both the apparent phase and
>>> magnitude drift is entirely consistent with analog-hardware temperature
>>>   effects, unrelated to clock stability, etc.
>>>
>>> Coax cables, for example, will change their loss characteristics and
>>> *effective length* with temperature, so with precise hardware like USRPs,
>>> it's
>>>   easy to see these effects.
>>>
>>> FMCW radar isn't my area of expertise, so hopefully others can comment
>>> on RX-processing strategies to deal with this, as it *must* also be a
>>> problem
>>>   with non-SDR FMCW radar implementations.
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Fri, Nov 28, 2014 at 12:08 PM, <mleech at ripnet.com> wrote:
>>>
>>>>  What is the magnitude of the frequency drift?
>>>>
>>>> What is the magnitude of the gain drift?
>>>>
>>>> What are you measuring backscatter *from*?
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On 2014-11-28 10:14, khalid.el-darymli via USRP-users wrote:
>>>>
>>>>   Hi,
>>>>
>>>>  Given a set of synced *(i.e., using external GPS REF/PPS)*,
>>>> time-commanded and calibrated *(i.e., through compensating for the
>>>> phase/mag offset between digital Tx chirp prior to transmission and ADC'ed
>>>> Rx signals) *N200 devices with LFTX/LFRX daughterboards, that work
>>>> with coherent LFMCW chirps, I am still seeing a tiny drift (both in the
>>>> magnitude and frequency) of the calibrated  back-scatter Rx chirp received
>>>> at time t1 when compared to an Rx chirp received at an earlier time t0.
>>>>
>>>>  The more the N200 device runs (e.g., 5 hours), the greater the drift
>>>> is. Obviously, this drift is pertinent to both the DAC and ADCs and the GPS
>>>> referenced clocks of the N200 devices.
>>>>
>>>> My questions are:
>>>>
>>>>  1- Why I still see such drift although my devices are synced with an
>>>> external GPS? and how do I correct for it?
>>>>
>>>> 2- Can the *PLL Carrier Tracking *block in GRC be used to track and
>>>> correct for such a drift? If so, how do I set the max/min freq inputs for
>>>> this block?
>>>>
>>>>  3- Can *AGC2* or *AGC3 *block be useful in this regard? If so, are
>>>> there any examples to explain how the input parameters of these blocks can
>>>> be set up?
>>>>
>>>>
>>>>  Thanks.
>>>>
>>>>  Best regards,
>>>> Khalid
>>>>
>>>>
>>>>  _______________________________________________
>>>> USRP-users mailing listUSRP-users at lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>>
>>>>
>>>
>>>
>>>
>>>
>>>
>>>  --
>>> Marcus Leech
>>> Principal Investigator
>>> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>>>
>>>
>>
>>
>>
>>
>>
>> --
>> Marcus Leech
>> Principal Investigator
>> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>>
>>
>
>
> --
>
>
>
>
> --
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20141202/47c17480/attachment-0002.html>


More information about the USRP-users mailing list