I too would be interested. The topic of common view GPS comes up every now and then. The incentive to use common view time transfer (CVTT) is reduced when plain old time transfer (TT) is so good already. Still, it's worth a try.
I'd be curious what level of improvement is possible. It will depend on the receiver and the antenna. I believe the NIST project uses fancy antennas but normal M12 receivers. So there's hope for the amateur. I don't think the TIC is that important: the sawtooth granularity is 1 ns so precision greater than that is wasted. One averages over many minutes anyway. Simulations would be a great idea. If you need raw data let me know. Google for CGGTTS and RINEX. Not all GPS receivers provide the level of per-satellite information required for common view. I know the M12 does, as well as high-end specialty timing receivers. I don't know if the Trimble TBolt or Res-t give out enough information to generate RINEX. But you can get the individual SV contribution to the solution using TBolt packet 0x8F-A7. /tvb ----- Original Message ----- From: "Lachlan Gunn" <lach...@twopif.net> To: <time-nuts@febo.com> Sent: Monday, April 15, 2013 5:27 PM Subject: Re: [time-nuts] Common-View GPS Network > My inclination is that one would need three things to participate in such a > system--- > > 1. A GPS receiver. > 2. A local reference oscillator. > 3. A way to measure their relative phase. > > I understand that the Thunderbolt can perform all of these functions, so > expect that this would be the favoured option for those without an Rb > oscillator. I do not have one, so will move on to the next setup. For > development the ResT could work the same way, but it's oscillator isn't as > good. So, we consider the next option. > > For those without a receiver that has itself a high-quality oscillator, the > next option would be to use a local reference and build a separate > phase-measurement circuit. I have already written a time-tagging system with > an FPGA, which could be reworked into what we need. This is probably > overboard, though, and might be achieved with a micro, possibly paired with a > PICTIC for the final interpolation. > > The next step would be to either transfer directly or to upload the phase > data to a central location where it could be processed together to estimate > everyone's offset to the average at once. > > A DMTD will be needed somewhere to evaluate performance, but this needs only > to be done somewhere rather than everywhere. > > Since there has been some interest I'll start whacking some simulations > together in the near future. > > Thanks, > Lachlan Gunn > > -------- Original message -------- > From: Mark Spencer <mspencer12...@yahoo.ca> > Date: > To: time-nuts@febo.com > Subject: Re: [time-nuts] Common-View GPS Network > > > > I'd be interested in understanding what it would take to participate in this > type of experiment. I'm unlikely to have any free time for this over the next > several months but if for example there was a particular GPS receiver that > was well suited for this type of work that would be useful info for me. > (Recently at work I've started to become involved with precision GPS location > systems and the claimed 3D accuracies that can be achieved using post > processing seem very impressive.) > Thanks in advance for any comments. > > > Regards > Mark Spencer > ------------------------------ > > Message: 6 > Date: Mon, 15 Apr 2013 22:49:38 +0200 > From: Magnus Danielson <mag...@rubidium.dyndns.org> > To: time-nuts@febo.com > Subject: Re: [time-nuts] Common-View GPS Network > Message-ID: <516c67e2.80...@rubidium.dyndns.org> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Lachlan, > > This would be fun to try with a few sites involved. It requires a fairly > decent GPS and antenna at each location, and loging and then > post-processing. Would be fun to see how well it can be made to perform. > > Cheers, > Magnus > > On 04/15/2013 02:55 PM, Lachlan Gunn wrote: >> Hello all. >> >> >> >> Having spent some time working over the last year on GPS time stability >> measurement, I'm keen to move onwards and upwards and have a go at >> common-view time transfer. While my receivers are in the post, I have >> thinking about my next direction. One thought that I have had is to try to >> write some software that can be used for real-time common-view (public if >> there is interest, but I am getting ahead of myself I think). >> >> My question to those in the know is whether they have found common-view to >> be useful over medium timescales (say, an hour or four). My understanding >> is that after a day or so the GPS signal itself becomes usable as a >> standard, so building a network is probably not tremendously useful over >> these sorts of time periods, but looking at such as figure 6 of [1], >> common-view should still be useful between a few minutes and hours. Has >> anyone here tried using such a method to produce their own short-term time >> scale, or is one better off just taking the simple route and tracking GPS >> time directly? >> >> >> >> Thanks, >> >> Lachlan >> >> >> >> >> >> [1] http://www.pttimeeting.org/archivemeetings/2008papers/paper45.pdf >> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
