1) They actually only need to be correct to within 10us, according to the spec.
2) Companies like endrun (www.endruntechnologies.com) make cute ($$$-y, though) and symmetricom make little CDMA time receivers that will get you ~10us accuracy indoors. Nice toys to have in your arsenal if you maintain time in machine rooms and don't like drilling through the ceiling. -Dave Daun Yeagley wrote: > Good explanation! > > Daun > N8ASB > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf > Of David I. Emery > Sent: Thursday, August 31, 2006 12:01 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Time syncing question > > On Wed, Aug 30, 2006 at 07:53:19PM -0500, Didier Juges wrote: >> I have observed that some cell phones set their clock when you power >> them up, and others set it at regular time. Some automatically change >> time zone as you travel and some don't, maybe due to the same process. >> >> Didier KO4BB > > I assume most members of this august group know that all CDMA cellphones > MUST know the correct time to within about 1 us or so in order to correctly > spread and despread the forward and reverse channel signals. > > There are mechanisms (pilot signals) built into the signaling format > that allow a CDMA cellphone with cheap TCXO time base to acquire the necessary > frequency and then time lock when it is first turned on or first sees a > signal. > > But a CDMA cellphone locked up on a base-station (its normal > state) should know the CDMA system time with microsecond accuracy and also be > able to correct its TCXO time base and lock it to the system reference so it > too > should be very accurate. > > And essentially ALL CDMA systems lock system time and frequency to > GPSDOs at the cell sites (easiest way of keeping a whole network of them > locked > together so handoffs work) and keep system time set to UTC. > > So the only thing preventing the clock on a CDMA cellphone from being > essentially arbitrarily accurate is laziness or sloppiness in the GUI firmware > that handles the visible clock display - in engine room in the bowels of the > phone there is VERY accurate time of day. > >> Glenn wrote: >>> _Most_ cell phones set their time to "network time." Usually within >>> one second. Although I have seen cell phones set themselves and be >>> off by nearly a minute. >>> >>> >> >> _______________________________________________ >> time-nuts mailing list >> [email protected] >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
