4 ms·
Don’t we have satellites broadcasting super accurate time, now?
by Redoubts 8y ago
Don’t we have satellites broadcasting super accurate time, now?
- owenmarshall 8y agoCourtesy of the US government.
- dewyatt 8y agoI have a wall clock that syncs from WWVB. It was pretty cheap and uses a single AA battery (which seems to last forever). I never have to update the time. Can satellite time provide an equivalent or better solution here?
- brianwawok 8y agoGPS could yes. Don’t know how many exist but would only add a few dollars in chips.
- owenmarshall 8y agoAnyone who has ever installed a GPS backed NTP appliance in a data center can quickly answer that. For those who haven’t: it involves drilling holes in the roof of your data center for a satellite antenna.
- Hello71 8y agodoesn't the wall work just as well?
- yardie 8y agoGPS requires line of sight to the satellites.
- reificator 8y agoAnd walls have two sides...
- __david__ 8y agoSo all your clocks need to be on outside walls?
- reificator 8y agoNo, but all your satellites would.
- yuubi 8y agoYou can see only about half the sky that way, which means usually getting almost as good a fix as with a roof mount antenna. For best results, you want the satellites to be as far apart as possible in the sky (measured by angle from your position, not miles between them). See https://en.wikipedia.org/wiki/Dilution_of_precision_(navigation) https://en.wikipedia.org/wiki/Dilution_of_precision_(navigat... . If you mainly care about time and can tolerate a few microseconds of error, usually being able to see 4 satellites might well be enough. I remember seeing a gps receiver designed just for time that could maintain sync using only one satellite (it assumed that it was bolted to an immovable object, and it might have needed to see 4 satellites at once at some point).
- myself248 8y agoNo, as I explain here: https://www.reddit.com/r/rfelectronics/comments/6nb6ky/do_cell_phones_receive_gps_signals_from_the_local/ https://www.reddit.com/r/rfelectronics/comments/6nb6ky/do_ce... To get halfway decent holdover performance, you want all the precision you can get when the constellation is good. That requires the best skyview (and least multipath) you can manage.
- vvanders 8y agoShortwave generally has much better propagation characteristics though buildings than gps.
- ddingus 8y agoWe have them, until we don't. Terrestrial AM Shortwave is super robust. And there is a ton of gear out there depending on it. The cost of the cut will be orders more than any savings. Worse, it will probably be turned right back on the moment saner heads prevail.
- tjohns 8y agoWe do. GPS is actually more accurate. That said... 1. GPS requires a clear line of sight to the sky. Doesn't work for indoor clocks. 2. Shortwave receivers are more energy efficient. 3. Redundancy is a good thing. Just in case GPS (or your receiver) has a problem. 4. WWV isn't just time. It also serves as a frequency reference for radio stations. It also transmits marine weather alerts, space weather (solar flares, etc.), and GPS system health updates. (Though apparently the marine weather notices are being discontinued in Jan 2019.)
- madengr 8y agoWWVB was a better reference due to surface wave propagation, but they added phase modulation which broke it as a frequency standard.
- nutcracker46 8y agoSatellites yes, and mobile phone infrastructure derives time and frequency from GNSS.