What about this: Use an NTP client running on a Smartphone. Such NTP clients are available for Pocket PCs, Symbian OS, etc.
Dominik Schneuwly -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak Sent: samedi, 20. août 2005 21:00 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Low cost synchronization Hi Mike, Sorry for the late reply. You raise an interesting question and here are some thoughts. > 1. Crystal Modeling Standard 32 kHz crystals won't work. TCXO aren't good enough either. OCXO are too power hungry. A couple of quartz wrist watches are good to 5 or 10 seconds per year. This may be close enough for your needs. The Pulsar PRS10 is one example. I think they use dual mode crystals to achieve their exceptional accuracy and relative temperature insensitivity. With the quantities you are talking about a dual mode crystal may fit the requirement. Dual-mode crystals are a niche market, however, so making arrangements with a manufacturer will not be simple. > 2. WWVB Receiver These are exceedingly cheap now and should fit all your requirements. Contact Rod Mack who has probably done more WWVB R&D than anyone on the list (he did the Ultralink receivers using Temic chips). Email me offline for his contact info. WWVB reception quality is not an issue since it's only used to intermittently re-synchronize the internal XO. One decent reception every couple of days or even weeks will take care of your requirements. Note also that many WWVB chipsets are now "global", meaning they will also receive signals from LF time services in Europe and Japan > 3. GPS Receiver > 4. GPS Time Receiver As many cell phones now include GPS receivers sizes and prices are dropping. But I'm guessing you are not going to meet your fob-size nor power specs with GPS (or other satellite nav systems). > 5. Cellular What percent of your thousands to millions of users world-wide already have a cell phone? To me this is the obvious solution. I would guess all cell phones know the time to a millisecond internally and this means a billion people on the planet are already carrying just what you need. Battery life is not a problem because all users already know how to recharge theirs. Now if each brand of cell phone would just have a standardized 1PPS output connector you'd be all set. > 6. TV Stations Two methods come to mind. The XDS timecode (used by PBS stations) is good in principle but perhaps not in practice. The other approach is to discipline a 32 kHz XO against the 3.58 MHz colorburst frequency. This seems dated, though. > 7. Atomic Reference In 10 years maybe. > 8. Other? 1) Look into an interface with Sirius/XM satellite radio. 2) Or piggy-back on the existing paging networks. 3) Lock onto the carrier of a high-power local AM or FM station. If these stations use Rb or GPSDO referenced carriers you'll get a long-term stable frequency for free. 3b) For extra credit use DSP. Since AM/FM radio and TV frequencies have assigned slots world-wide you can simultaneously receive many local stations and combine their frequency stabilities to a common mean time/frequency. This would make a wonderful project for someone; commercial or university. For any solutions that give you stable frequency only (XO, RF carriers, 60 Hz) you will need a way to set the initial time and to reset the time when the batteries fail. For any solutions that give you time only you will presumably need to convert from UTC to local time. Also, are you concerned with DST? At least with your requirements, you don't have to worry about leap seconds! /tvb http://www.LeapSecond.com _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts