[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 11:31:36 EST 2014


I see. Thanks for the information. It seems the temp sensor incorporated in
the QR210 is also for the 'ambient temperature', similar to your
suggestion, right?
http://www.ettus.com/kb/detail/qr210-architecture-and-overview

Khalid



On Tue, Dec 2, 2014 at 12:43 PM, Marcus D. Leech <mleech at ripnet.com> wrote:

>  On 12/02/2014 11:02 AM, khalid.el-darymli wrote:
>
>  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
>
>  With the exception of the TVRRX2, there are no internal temperature
> sensors in USRP hardware.  That's why I suggested a separate device, placed
>   inside the N210 cabinet to be used as a proxy.  There are very few
> electronic components that provide an "internal temperature" output as
>   a kind of monitoring thing.  Particularly in the analog RF space.  Some
> computer motherboards have this, but it's not an inherent property of
>   electronics to provide a temperature output as a side effect or anything.
>
>
>
>
> 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
>>
>>
>
>
> --
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>
>
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