Hi Yes you could. If you are listening to them by ear, something in the ~100 ms range is probably a good guess in terms of precision. There are also propagation issues that may come in with a broadcast system.
If you are still after 0.1 ppm, that gets you out to a million seconds per adjustment attempt. Roughly two weeks between attempts is about where that would put you. At that sort of time period you *would* get a lot of local temperature profile averaged into the result. I’d say that’s a good thing. ==== One very basic question on all of this: If the TCXO is the expensive part of the system and GPS modules are (relatively) cheap …. why use the TCXO at all? Simply run a crystal as the reference. Do a drop / add to keep things running right. When the GPS has lock, you have perfect time sync, When it drops out, you go to the crystal as a backup. If microsecond level accuracy *is* what the goal is, the TCXO, even when it’s calibrated is not a really good way to do that ... Bob > On Apr 13, 2018, at 9:02 PM, Adrian Godwin <artgod...@gmail.com> wrote: > > Could you use the "pips" instead of a PPS signal, again comparing them some > weeks apart to give a long reference time ? > > https://en.wikipedia.org/wiki/Greenwich_Time_Signal > > If your local radio broadcaster doesn't play something like them, they > could probably be generated with a web application. > > > On Sat, Apr 14, 2018 at 12:13 AM, Wayne Holder <wayne.hol...@gmail.com> > wrote: > >> Again, thanks for all the great feedback and suggestions. >> >>> Are you familiar with these devices which I just found this week? >>> https://tentaclesync.com/products >> >> Yes, that's one of the lower cost commercial units available. Another is >> the NanoLockiIt by Ambient >> <https://www.bhphotovideo.com/c/product/1333498-REG/ambient_ >> recording_acn_nl_nanolockit_miniature_timecode_synchronizer.html>, >> which is company that's been making timecode products for many years. >> Compared to more traditional prices for timecode generators, these are >> relatively inexpensive at about $300. However you need at least two, or >> more generators to be useful, so that adds up pretty fast for an amateur >> videographer, or starving film school student. In contrast, BOM for the >> design I'm working on is less than $30 (the TCVCXO being, by far, the >> most expensive part.) >> >> My plan is to also write a desktop application, probably in Java to make it >> portable, that the person building the devices could use to perform the >> initial calibration and also setup various options. So, the NTP-based >> solution is attractive in that it doesn't require any additional hardware. >> I'm a Mac user so, after a bit of reading the NTP implementation on the >> Mac, I tried a few experiments. Typing "ntpq -p" in the terminal >> app produced this response: >> >> remote refid st t when poll reach delay offset >> jitter >> >> ============================================================ >> ================== >> >> *usdal2-ntp-001. .GPSs. 1 u 428 1024 377 51.131 1.944 >> 1.153 >> >> and typing "ntpq -c rl" printed out: >> >> associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync, >> >> version="ntpd 4.2.8p6@1.3265 Fri Feb 5 17:38:17 UTC 2016 (124.60.2~39)", >> >> processor="x86_64", system="Darwin/16.7.0", leap=00, stratum=2, >> >> precision=-20, rootdelay=51.131, rootdisp=34.160, refid=17.253.2.125, >> >> reftime=de7ba9c1.937e5f86 Fri, Apr 13 2018 15:12:17.576, >> >> clock=de7badf7.39f8d36a Fri, Apr 13 2018 15:30:15.226, peer=7077, tc=10, >> >> mintc=3, offset=1.944153, frequency=25.163, sys_jitter=0.000000, >> >> clk_jitter=0.745, clk_wander=0.001 >> >> I believe that the "precision" of -20 value on the 4th line is supposed to >> be interpreted as 2^-20 seconds which, if my math is correct, works out to >> be a precision of about 1 PPM. Is that correct? If so, it would seem like >> I should be able to use my system's internal clock to perform a "tweak" in >> around 10,000 seconds, or a little less than 3 hours. Does this seem >> correct, or have I missed something? >> >> Alternately, if I included a GPS receiver in the design, the whole process >> could be done within the device, which would probably be the easiest >> approach to calibration for the person building one. This would increase >> the cost and make the device larger, but users could then maintain >> calibration by periodically keeping them plugged in for a few hours. Or, >> perhaps I could just design a 2nd board for a GPS "calibrator" module that >> could be plugged into the timecode generators to calibrate them. Hmm... >> lots to think about. >> >> Wayne >> _______________________________________________ >> 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. _______________________________________________ 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.