Hi Marcus, Is there a temperature sensor on-board the N200 unit? If not, does it support installing any such sensor?
Thanks. Best regards, Khalid On Fri, Nov 28, 2014 at 5:44 PM, Marcus D. Leech <mle...@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, <mle...@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@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 > >
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