In this PDF there are examples in MATLAB for the C/A code generation, FFT search, acquisition, carrier pull-in and tracking. <http://www.sm.luth.se/csee/courses/sms/019/1998/navstar/navstar.pdf> On Tue, Aug 21, 2018 at 2:31 AM Attila Kinali <[email protected]> wrote: > > On Mon, 20 Aug 2018 11:46:15 +0200 > Nicolas Braud-Santoni <[email protected]> wrote: > > > On Mon, Aug 20, 2018 at 01:15:10AM +0200, Attila Kinali wrote: > > > The online shop still works pretty well, as far as I am aware of. > > > If you order more than 10-20 LEA/NEO modules, I recommend going > > > through the u-blox sales. They might not resopond to you as quickly > > > as one would like but they should still give you a decent offer. > > > > They do not have the UBX-M8030-KT-FT in the shop, but perhaps I should try > > and modify a NEO module as you suggested. > > Ah.. you want to go for the chip. That explains why u-blox isn't selling > to yo directly. The chips have minimum quantity of a single reel which > is IIRC 1000 pieces. > Keep in mind that the information needed to programm it is only available > under NDA. > > > > One month? If you are not using a Cs beam standard, then having > > > an integration time of a month is pretty pointless. > > > > The issue is that I only get a measurement every second, with a fairly-large > > amount of noise, so it takes a while to get enough samples until the noise > > averages down to below the oscillator's own noise. > > (Hence why I want to move to carrier-phase measurements; a better receiver > > would definitely help, though) > > Uhm... after saw-tooth correction the PPS jitter should be less than 10ns. > That translates to an uncertainty of 1e-8. As PPS noise is pretty much > uniformly distributed (whith curtains that resemble white noise), you > can average it and get a square root improvement. So at 10s you would > be down to 3e-10 uncertainty, which is about what a decent TCXO > does provide at 10s (if I'm not mistaken). So, either you are using > something different than a TCXO or your PPS noise is higher than it > should be under good conditions. > > > > I mis-spoke, though, one month was how long it took, with a particular set > > of > > parameters, to get a PLL lock from a cold start (i.e. without the Kalman > > filter > > being seeded with previous measurements); I guess that what I get when > > writing > > late at night. :) > > That sounds like you got the control loop wrong :-) > Even if you don't do anything fancy (like switching control loop modes) > to assist faster locking, with a loop time constant of a few 10s (which > is what you should do for a TCXO), your loop should lock in a few 100s, > at latest in 1000-2000s. > > > > > > I was able to work around the problem in part, by dynamically adjusting > > > > the > > > > constants of my IIR (and so the integration time), and it works pretty > > > > OK > > > > despite being highly non-linear, but there is only so much one can do > > > > when > > > > fixing hardware deficiencies in software. :( > > > > > > Hmm? What kind of problems? > > > > “The problem” in question was the trade-off between precision and the time > > it > > takes for the PLL to lock. > > The trade-off between precision and locking time does not happen at the > PLL, but at the choice of your local oscillator. The reference oscillator > defines what your loop time constant should be, 10-20s for an XO, 10-100s > for a TCXO, 100-3000s for an OCXO, 10ks-300ks for an Rb. Your locking time > is then just a (small) constant factor larger than your loop time constant > if you don't do any adaptive control (disclaimer: this is a very simplified > view of designing a control loop). > > > > > - Trying to make a good GPSDO is hard enough as-is ;) > > > > > > Not really. You just need to understand what the limitations of the > > > components are and how to design a proper control loop. That's why > > > Trimble GPSDOs or the Star-4 work so well. They were designed by > > > people who know these things. > > > > I'm keenly aware; I was saying that I don't have the same expertise as > > Trimble's engineer, so there is a bunch of learning involved. > > Most of this can be learned just by reading GPSDO manuals, GPSDO schematics > and the time-nuts archives :-) > > What you need to know is: > 1) How GPS works and what the uncertainties are > 2) How your reference oscillator behaves > 3) How to design a control loop > > The GPS knowledge is a bit hard to come by as there are not so many > good web resources on it. I recommend reading books like those from > Misra/Enge[1] and Kaplan/Hegarty[2]. Those two give in-depth knowlege > on the system as they explain how to build a receiver, with the Kaplan > one being easier to understand for a first read as it doesn't dwell > as much on theory as Misra. In addition to those two I would go for > Parkinson[3], which explains how GPS as an overall system works and > performs. > > For your oscillator, I would have a look at NIST TN 1337[4] and > NIST SP 1065[5]. Those two explain what stability of oscillators > is and how you should talk about it. And especially how you compare it. > > For control loops, I usually recommend Franklin's book[6], which > gives a good introduction, but does not cover any of the advanced > topics which you will need for a GPSDO. But even just the basics > will get you to a working system. It might not perform optimally > under all conditions, but it should do quite well. > > > Attila Kinali > > [1] "Global positioning system signals, measurements, and performance", > 2nd edition, by Misra and Enge, 2012 > > [2] "Understanding GPS : principles and applications" > 2nd edition, by Kaplan and Hegarty, 2006 > > [3] "Global positioning system - Theory and Application", Volume 1 & 2, > by Parkinson, Spilker, Axelrad and Enge, 1996 > > [4] "Characterisation of Clocks and Oscillators", NIST Technical Note 1337, > by Sullivan, Allan, Howe, Walls, 1990 > > [5] "Handbook of Frequency Stability Analysis", NIST Special Publication 1065 > by Riley, 2008 > > [6] "Feedback Control of Dynamic Systems", by Franklin, Powell and > Emami-Naeini > > -- > <JaberWorky> The bad part of Zurich is where the degenerates > throw DARK chocolate at you. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.
_______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
