[time-nuts] Smart Phone time display accuracy...?

[Dave B]

On 17/03/17 00:03, Mike Baker wrote:
> Hello, Time-nutters--
>
> Any thoughts on what the likely accuracy of smart phone time
> displays might be?   I am thinking that the stacking of delays
> along the path to its receive antenna plus any internal processing
> delays would accumulate to some unknown degree.  Any
> thoughts on this?
>
> Mike Baker

Well..

Both the Android phones I carry (my Motorola "MoTo G", and a Samsung S6
for work, on different carriers here in the UK) are visually spot on
with the Thunderbolt and Lady Heather's display, and with the various
PC's I have NTP'd to the pool, or my local NTP server, and also with the
BBC time signal on Analogue FM radio, and the various HF time-signal
broadcasts.

However...

How would you get a low latency "time event" out of a phone to test it
against something else, without introducing other indeterminate delays?

I have in the past "Attempted" to use NTP over a mobile internet link,
with terrible results.  When it did get a response from a time server,
the jitter was truly awful, in the multiple 10's of milliseconds range,
and that was from a fixed location in the clear, with a good phone signal.

As others have said, the GSM/3G network uses accurate timings
internally, so probably the handsets do maintain good sync to that, and
to whatever root standard the overall system is synced to.   Be it GPS
or ???

AndroiTS GPS Test (V 1.48 Free) is good, but a battery hog I find.   On
my Moto G, I find that it can handle not only the US GPS system, but
three other systems too, including Glonass, and I think the new Chinese
system.  I don't recognise the last symbol, maybe Galileo.  Not bad for
a consumer gadget.

I do not know if the phones could use GPS time directly, but that's only
a software task at a guess.

Regards.

Dave B.
G0WBX.