[time-nuts] Cell Phone time ?

John Miles jmiles at pop.net
Sun Nov 25 19:34:34 EST 2007

I doubt it's possible to make any general statements about the accuracy of
the time display on a phone.  It updates whenever the firmware gets the
proverbial round-tuit time slice.

My old phone, a Motorola flip-phone variant of some kind, was always dead-on
versus the Thunderbolt on Qwest's Seattle-area CDMA network.  But it had
nothing to do but sit there and mark time.  My current phone is an iPhone on
the AT&T GSM/EDGE network, and it seems to lag about 7 seconds behind UTC as
reported by the Datum 9390.  That puts it 21 seconds behind GPS time as
reported by the Thunderbolt.

It doesn't appear to make a difference whether it's connected or not.

-- john, KE5FX

> Well, this may seem like a dumb question to some of you, but, it does have
> me baffled a little. I have noticed some time ago that the time
> indicated on
> my cell phone is usually two to four seconds ahead of GPS time. I
> was under
> the impressions that most towers did use GPS time. Anyway, I
> wrote it off to
> thinking that the phone is free running unless connected to a
> call and hence
> the drift. I even tried this theory by dialing my cell phone from my land
> line, and low and behold, the times matched with GPS as long as I was
> connected. Soon as I disconnected it was immediately off 4 seconds and
> eventually settled at about 2 seconds. Since there is a signal
> indicator on
> the cell phone that is active all of the time, it is obviously receiving
> something from a local tower. Could that signal not have GPS time embedded
> in it? It must have some, since going from one time zone to the other
> switches the cell phone time automatically, but obviously not
> accurately. It
> seems like a 2 second window is pretty large to search to make
> all of those
> bits line up so one can talk, or to even have the phone ring.
> Thanks for any
> help in making me understand this small dilemma. Regards - Mike

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