Hi Bob, yes I'm including several other sources and usually about 3 are getting included in the discipline of the local clock. Here is my ntpq -pcrl output at the time I wrote this message.
pi@raspi2 ~ $ ntpq -pcrl remote refid st t when poll reach delay offset jitter ============================================================================== LOCAL(0) .LOCL. 10 l 20h 64 0 0.000 0.000 0.000 oGPS_ONCORE(0) .GPS. 0 l 13 16 377 0.000 0.000 0.002 +time-c.timefreq .ACTS. 1 u 2 64 377 21.373 -0.344 0.504 +utcnist2.colora .ACTS. 1 u 3 64 377 22.262 0.144 1.720 +india.colorado. .NIST. 1 u 48 64 377 22.236 0.188 0.122 -time-a.timefreq .ACTS. 1 u 27 64 377 21.566 -0.595 0.405 associd=0 status=0419 leap_none, sync_uhf_radio, 1 event, leap_armed, version="ntpd 4.3.37@1.2483-o Thu Jun 11 00:12:07 UTC 2015 (1)", processor="armv7l", system="Linux/3.18.14-v7+", leap=00, stratum=1, precision=-19, rootdelay=0.000, rootdisp=1.195, refid=GPS, reftime=d9246d02.38389bc3 Thu, Jun 11 2015 14:24:34.219, clock=d9246d0f.92141a9c Thu, Jun 11 2015 14:24:47.570, peer=6887, tc=4, mintc=3, offset=0.000163, frequency=-7.742, sys_jitter=0.001907, clk_jitter=0.002, clk_wander=0.000, tai=35, leapsec=201507010000, expire=201512280000 I have been careful to try and tweak the time1 offset to get a reasonable offset against the reference servers that show something less than 1ms over time. Shortly I'll have another GPS / M12+ up and running on another PI that I can use as a local reference along with other NTP servers over the internet. As you can see, the PPM frequency on this Pi is still showing -7.742. I assume that is if it was undisciplined? I have wondered about that. Matt On Thu, Jun 11, 2015 at 4:59 AM, Bob Camp <kb...@n1k.org> wrote: > Hi > > Be careful of “single source” comparisons. When running with one reference, > NTP is really measuring the reference against it’s self. It’s analogous to > using a > frequency counter to check it’s own reference. It *does* indeed check a > number of things. > It’s not really checking everything. > > An overly simple way to look at it: > > NTP is running a PLL, it “locks” a (software based) oscillator to the > reference. With > a single reference, it’s comparing the output of that PLL to the input to > the PLL. > > The obvious way to get around this is to have multiple references coming > into NTP. > That’s easy if you want “less stable” references. It’s more money if you > want to > duplicate the GPS you have. After that it’s a matter of telling NTP which > sources > to discipline to and which to simply observe. > > Bob > > > On Jun 11, 2015, at 12:05 AM, M. George <m.matthew.geo...@gmail.com> > wrote: > > > > Here is what I have been able to do with a Motorola Oncore UT+ that I got > > from Bob Stewart awhile back. This is with a Raspberry PI 2 with a > number > > of tweaks and a custom compiled kernel. Nothing too drastic... plus the > > current Dev version of NTP compile on the Raspberry PI. I'm getting > better > > results letting ntpd discipline the clock over doing kernel discipline... > > not surprising because the algorithms in the ntpd code are much more > > sophisticated than the Linux kernel pps code... ntpd discipline provides > > much lower jitter in my experience. > > > > I'm rambling at this point, but the following samples are with a $30 > > antenna on the peak of my roof with LMR-400 solid conductor coax at a > > length of 70 ft. ~1.2 ns per foot delay based on the LMR-400 specs and > > nice low loss. I'm running the coax into an 8 way antenna splitter > etc... > > nothing that anyone else hasn't done before here. > > > > The Raspberry PI 2 in this case is under load too as part of the > > www.pool.ntp.org pool: time.nc7j.com if you want to sync against it. > > > > As everyone else has mentioned, it's total overkill for NTP, but I'm just > > interested in tweaking and seeing how good I can get for fun more than > > anything else... i.e. time-nut obsession. I'm pretty happy with the > > following under load with www.pool.ntp.org set at 25MB of bandwidth > which > > controls the traffic to my Pi 2 running NTP. It's taking a lot of > traffic > > per second... the CPU for ntpd on the Pi is still low at around .5% to 1% > > of one core on the Pi 2. > > > > Here is a block of offsets from a loopstat file, and yes I cherry picked > a > > nice block in the low nano seconds, but it rarely shows an offset into > the > > micro seconds over time.. these are 16 second samples of the offsets... > > > > -0.000000225 > > -0.000000273 > > 0.000000094 > > 0.000000328 > > -0.000000155 > > -0.000000042 > > -0.000000169 > > 0.000000323 > > 0.000000038 > > -0.000000312 > > -0.000000675 > > -0.000000036 > > 0.000000213 > > -0.000000193 > > 0.000000005 > > -0.000000503 > > -0.000000154 > > -0.000000179 > > -0.000000321 > > 0.000000096 > > -0.000000119 > > -0.000000173 > > > > Not too shabby for a killer deal on an Oncore UT+ for $5 from Bob! I'm > > running the PPS out of the UT+ through a level converter to get the ~3.3v > > PPS output... the serial output on the UT+ is also going through a level > > converter direct into the Pi 2. Using the oncore 127.127.30.0 ntpd > driver > > and again, i'm not using hardpps kernel discipline. > > > > Anyway, users on the other end are at the mercy of the network latency > and > > noise etc... but I'm serving up some pretty consistent time references, > > considering the Pi 2 was $35... and the only one that really cares is > > me... I'm trying to masquerade as a nerdy wana-b time-nut. > > > > I think NTP is a great place to start... if you want to toy around and > > tinker, plus provide a service to the rest of the Internet by joining > > www.pool.ntp.org and sharing your obsession with time. > > > > Max NG7M > > _______________________________________________ > > 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. > > _______________________________________________ > 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. > -- M. George _______________________________________________ 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.