[time-nuts] Re: Where do people get the time?

[Bob kb8tq]

Hi

Back a while ago, Symmetricom came out with a series of cell disciplined oscillators.
Some had Rb’s in them, a few had OCXO’s. More or less, the idea was to have a 
GPSDO equivalent device that could be deployed without the antenna hassles that
GPS can entail. 

After a few years, they pretty much dropped the product line and lots and lots of the
boxes started showing up on eBay. Many folks got PRS-10 Rb’s by pulling them out
of some of the boxes. 

What happened? 

Cell systems *should* be synchronized. The collision avoidance side of the transmit
waveforms may depend on this. The assumption was that everybody putting up a 
system would tie it to GPS and keep it fully locked. Turns out that was a bad assumption. 
Folks running systems that had no “neighbors” simply ignored the synch stuff. They 
let the system free run. Nobody complained and it just went on and on that way. 

Synchronizing the time stamp that your cell device gets is a few levels up from the
sync of the transmit waveforms. It’s a good bet that if they aren’t worrying about the
transmit stuff, the time stamps they sent you are not the greatest …..

Very much YMMV ….

Bob

> On Dec 27, 2021, at 2:10 PM, Adam Space <time.isanapp at gmail.com> wrote:
> 
> As a younger person I appreciate this write-up. It is interesting to see
> the progression. Nowadays, phones are synchronized to within a second
> easily, and probably within 10ms at least once per day (this is what I
> suspect from occasionally checking the offset on my phone). With computers
> too, I would bet that most come out of the box with some sort of NTP setup
> that at the very least keeps them within a few seconds, depending on how
> often the default polling interval is. The idea of having to go to great
> lengths to get access to an accurate time signal seems foreign today, but
> it's interesting hearing about that being the case in the past.
> 
> On Sat, Dec 25, 2021 at 8:07 PM Attila Kinali <attila at kinali.ch> wrote:
> 
>> On Sat, 25 Dec 2021 15:27:51 -0800
>> Hal Murray <halmurray at sonic.net> wrote:
>> 
>>> How good are cell phones?  I remember comments about them being way
>> off.  But
>>> that was a long time ago.
>> 
>> Cellphone network time distribution is something rather new
>> and didn't exist until EDGE (or was it HSDPA?) came along.
>> But once it was available, it was "good enough", i.e. the
>> time offset was low enough to be not perceivable (~100ms).
>> At least in Europe.
>> 
>> I know from other countries, that back in 2005, network time
>> was off by a few minutes. This has probably improved now, because
>> UMTS requires the cells to be synchronized to UTC to within
>> a few 10s of µs. (I don't remember the details, Magnus can
>> provide a more accurate picture) And by already having accurate
>> time in the network, providing that to the cellphones is easy
>> and the obvious way to go about.
>> 
>> 
>>> If I was doing it now, I would probably setup one of the battery powered
>>> clocks that listens to WWVB.  When were they first widely available?
>> 
>> Hmm... Let me give you a quick history of how time aquisition
>> evolved through the eyes of a fledgling time-nut :-)
>> 
>> Disclaimer: This is how I experienced things as I grew up in
>> Switzerland. It was probably quite similar throughout western
>> Europe, but I didn't travel enough until early/mid 90s to say
>> anything beyond the countries I visited regularly. Not to
>> mention that a toddler who can't read a watch wasn't much
>> interested in how to get accurate time in the first place...
>> That said, Swiss were and still are quite a bit more obsessed
>> with time than the rest of Europe. So my view might be a bit
>> skewed.
>> 
>> In the 80s virtually all watches and clocks were quartz movements.
>> I.e. they kept time accurately enough for most things. There were
>> still some mechanical watches around, but they were mostly a
>> thing of the past and kind of a fashion statement... Or a watch
>> gifted by a relative decades ago. Most people set their watches
>> at least every 6 months, when dailight saving switched. I had
>> (and lost) a Swatch Flick Flak (
>> https://www.newlyswissed.com/wp-content/uploads/2015/08/Flik-Flak.jpg ),
>> two Pop Swatch ( https://www.uhrenkosmos.com/30-jahre-pop-swatch/ )
>> and two Tissot Two-timer (pretty much this model
>> https://watchcharts.com/listing/1084976/tissot-twotimer-timer-analog-digital-watch
>> ).
>> as my watches as a kid during kindergarten and elementary school.
>> The Tissot I used until I broke its wristband holder a week before
>> I graduated from high-school, which had a pretty deep gouge in the
>> glass through the whole watch face when I fell on some gravel path
>> in 4th grade.
>> 
>> None of these watches were special for a child in Switzerland.
>> Even the Tissot Two-timer, which was IIRC CHF 80-100 back in
>> the late 80s (probably around 200 USD in today's money), was a
>> relatively common watch to have as an elementary/middle school
>> student. And even a first grade student was expected to have
>> some form of a watch, either on his wrist or in his pocket.
>> And that, even though there was a clock somewhere in sight virtually
>> everywhere in Switzerland  as there were plenty of watch/clock shops
>> and a lot of stores had a clock somewhere around the entrance.
>> 
>> The way to get time was usually TV and radio broadcast or church
>> bell towers. One popular way was to adjust to the beep at the
>> start of the news, which was always scheduled at fixed time
>> (usually the start of the hour).
>> 
>> But using Teletext ( https://en.wikipedia.org/wiki/Teletext )
>> was more common, whenever a TV was available, as it offered to
>> have time without waiting for a special program and could be
>> read with sub-seconds accuracy. What was a bit weird, now that
>> I think back, is that different TV stations had slightly
>> different times. Usually just a few seconds, but enough to
>> be noticable. I usually set my watch whenever I noticed that
>> it was off more than 30-60 seconds (usually because I would
>> start missing the bus). Which was, if I remember correctly,
>> every 3-4 months with the Tissot.
>> 
>> The clocks of churches and schools were, in the 80s, already
>> synched up to HBG or DCF77, though I did not know that back then.
>> I just saw the big blinkenlights that would control the clocks
>> and would wonder why they were so big. :-)
>> 
>> In the late 80s, DCF77 alarm clocks became cheap and very common.
>> And we started using them as a quick reference instead of the TV.
>> They also had the advantage of always showing the time, which made
>> checking the accuracy of one's watch kind of an automatic and
>> regularly performed movement. Their range was quite impressive too.
>> I once took one to Turkey and it would still sync up during the
>> night. (I completely forgot that I left it there with a relative
>> until it turned up a few years ago, still working).
>> 
>> In the late 90s, early 2000s, the internet became more ubiquitous
>> and people started to use NTP to sync their computers and then
>> set their watches according to their computers. At least those
>> of us who were using Unix/Linux. It would take another couple
>> of years, until Windows would offer something similar out of
>> the box, though it would take IIRC until Windows Vista for it
>> to be accurate for better than 10 seconds (which lead to interesting
>> effects when using concurent document editing through Active
>> Directory). Also around the same time, everyone and their dog started
>> to have a cell phone. While at first one had to manualy set the
>> time (the same way as a watch), at some point in the first half
>> of the 2000s, the cellphone network started to provide time.
>> 
>> Today, for most people, their cellphone is the thing that provides
>> them with accurate time to which they set ther watches and clocks.
>> 
>> For me, my main clock source is NTP, for the most part. At least
>> for everything that is networked. I do have a GPSDO that provides
>> me with an accurate PPS for my time-nutty needs, but that is only
>> used within my home network and for measurement. I set my watches
>> twice a year, when I have to adjust them for daylight savings,
>> by which time they are usually off by less than 10s. (Modern
>> quartz watches are amazing!)
>> 
>>                        Attila Kinali
>> 
>> --
>> The driving force behind research is the question: "Why?"
>> There are things we don't understand and things we always
>> wonder about. And that's why we do research.
>>                -- Kobayashi Makoto
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