On 05/24/2017 11:37 AM, Tate Belden wrote: > Warren, one slight correction on an other wise nicely written bit of info: > > The time transmitted from WWV is not Mountain Time. Even though the WWV > transmitter farm is located in the Mountain time zone, the signals are > transmitted as "Coordinated Universal time", UTC, or 'Zulu' time. > > Here, you can listen to a recording made at the transmitter site for the > 5Mhz signal: > https://ia802605.us.archive.org/24/items/WWV5MHz/WWV-5MHz.MP3 I remember listening to this on a shortwave radio back around '62... > > On Wed, May 24, 2017 at 8:36 AM, Warren Young <warren at etr-usa.com> wrote: > >> On May 24, 2017, at 7:53 AM, Chris Olson <chris_e_olson at yahoo.com> wrote: >>> One of our STEM interns recently observed that there are >>> inexpensive clocks that sync via radio to standard time >>> services. >> There are two major types: >> >> 1. WWVB and its equivalents in other countries: >> >> https://en.wikipedia.org/wiki/WWVB >> >> 2. GPS clocks. >> >> >> WWVB has several problems: >> >> a. It’s transmitting from a fixed location in a time zone you probably >> aren’t in — US Mountain — being the least populous of the lower 48’s four >> time zones. You therefore have to configure time zone offset and DST >> rules, which means additional software if you want it to track changes to >> these things. There were 10 batches of such changes last year! >> >> https://mm.icann.org/pipermail/tz-announce/2016-November/thread.html >> >> b. It’s a weak signal. Unless you’ve got a big antenna or are positioning >> the receiving device near a window, you probably can’t receive the WWVB >> signal reliably. >> >> c. Computers have major RFI shielding problems, which is why they’re >> typically placed in metal boxes. (Even plastic-cased laptops have metal >> boxes inside.) That means you have to have an external antenna even in the >> best case. Now apply what you know about Wifi reliability to the problem >> of receiving a signal from a different *time zone*. >> >> I happen to be in the Mountain time zone, and it doesn’t take too much to >> shield our WWVB clocks from the signal. I can only imagine how much easier >> it is out on the coasts. >> >> >> GPS time is a much better solution, but it’s power-hungry, as you probably >> know from running GPS on your smartphone. This rules it out for laptops. >> >> The GPS transmitters probably have a higher received signal strength than >> WWVB, but cinderblock walls and grids of 42U equipment racks block the GPS >> signal quite well. This is why data centers with such clocks generally >> have to run an antenna to the outside for their clock. That makes it far >> more expensive than just connecting to an upstream NTP server. >> >>> When I was a student, such questions would have earned me >>> extra homework assignments. >> So do I get an “A”? :) >> _______________________________________________ >> CentOS mailing list >> CentOS at centos.org >> https://lists.centos.org/mailman/listinfo/centos >> > >