elfchief-timenuts@lupine.org said: > Are there currently any decent (intended (or at least usable) for > timekeeping) GPSs that support using L2/L5 for this purpose? Google is > turning up lots of nothing, for me... I don't know of any. I'm somewhat sure that they don't exist or maybe they are hidden in the military sector. Tom Clark and Rick Hambly work on timing for VLBI. They run a yearly workshop on timing. Their slides are available on the web. They use low cost L1 gear. I'm sure they would use something better if it were available commercially. They are starting with Hydrogen Masers so cost cutting on the GPS receiver would not be a problem. -- These are my opinions. I hate spam.

-------- In message <20160315031836.0F5B3406057@ip-64-139-1-69.sjc.megapath.net>, Hal Mu rray writes: >Tom Clark and Rick Hambly work on timing for VLBI. [...] They use low >cost L1 gear. The crux of this seems to be that getting better time information out of multiple bands *in real time* is not a solved problem. If/when you solve it, you would still have the problem of how to electrically instantiate that time information in the picosecond domain. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

Hal, One point being missed here is that when you get to high-end, dual-frequency (L1/L2), carrier-phase GPS there's often less need for real-time results. The receivers are run more in a data logging mode. Many sites collect data continuously and then apply GPS corrections hours to days later, as they are computed and refined by world-wide networks, such as http://www.igs.org/ . In other words, the goal is not so much to steer your clock as is done with a GPSDO, but simply to know how far off your clock is; even if that means waiting a few days for all the calculations to settle. They are run in a mode of "what time was it" rather than "what time is it". For really good clocks this is a better way to do timing. A GPSDO can only steer based on recent past and present data, using the rough broadcast values of SV clock & position. But when you post-process with high-end receivers you get to use past, present, and future data. The SV clock and orbit data you use are significantly more precise, because it's calculated from hundreds or thousands of GPS sites world-wide. Plus there's no DAC or EFC or h/w noise or tempco; "paper clocks" avoid all of this. For applications like what Tom & Rick (VLBI) are involved in, there's no particular need for the H-maser to have the "right" time or be at the "right" frequency. All that's needed is a record of what the time/frequency offsets are. Those kind of clocks tend to be left alone. /tvb ----- Original Message ----- From: "Hal Murray" <hmurray@megapathdsl.net> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Cc: <hmurray@megapathdsl.net> Sent: Monday, March 14, 2016 8:18 PM Subject: Re: [time-nuts] Conditioning Rubidium Oscillators > > elfchief-timenuts@lupine.org said: >> Are there currently any decent (intended (or at least usable) for >> timekeeping) GPSs that support using L2/L5 for this purpose? Google is >> turning up lots of nothing, for me... > > I don't know of any. I'm somewhat sure that they don't exist or maybe they > are hidden in the military sector. > > Tom Clark and Rick Hambly work on timing for VLBI. They run a yearly > workshop on timing. Their slides are available on the web. They use low > cost L1 gear. I'm sure they would use something better if it were available > commercially. They are starting with Hydrogen Masers so cost cutting on the > GPS receiver would not be a problem. > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > 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.