OT accurate time checks?

[Nick Odell]

I think it's considered okay to talk over the chimes of BB after the first couple because they go on so looooong. "Crashing the Pips" is a no-no.

Nick

[Capn Nemo]

:-)

"AboutTime Home Page Current Version: 4.8 (11/19/1999) NOTE for Windows XP and Vista:

AboutTime isn't really needed on Windows XP, which has its own way to set the system clock (although some loyal users report AboutTime works better than the XP service), and it will only work on Windows Vista by disabling some of its security features."

[The Natural Philosopher]

seconds. Such tolerances are outside the design specification of the W32Time service.'

so insatll something better like this

[Harry Bloomfield]

Moonraker used his keyboard to write :

Big Ben is not really that accurate, so for the radio they use a recording which is accurate - or used to be. Now it can be less accurate due to digital links in the transmission system.

Windows draws it time data from an Internet Time Server, of which there are several. So assuming you set your PC to sync itself fairly frequently, it should be near enough. Possible errors are delays in the time packet delivery, but I understand Windows checks and compensates for these delays before calibrating its clock.

Your GPS's time should be spot on, assuming it has lock with the satellites, though there might be delays in the software.

If you want continuous accuracy, then you need to monitor MSF, which transmits an accurate time signal once per minute. MSF is what is used for setting radio clocks and watches, but they only usually sync themselves once per 24 hours, assuming they manage to receive the signal. MSF transmits (60Khz) not only an accurate time signal, but a complete set of data for time, date including the year, in every complete minute via a 1 bit per second, plus a fast code 'croak' set of date in the final second. I wear a MSF controlled solar powered watch, have several MSF controlled clocks and have a weather station which also syncs itself to MSF. In the 70's I wrote software to continuously decode and continuously display the MSF time, from Rugby. I had to write to GPO MSF Rugby and beg for a spec for the data format, to be able to decode it :D

[Harry Bloomfield]

John Williamson was thinking very hard :

They would use a cuckoo clock lol

[Harry Bloomfield]

Martin Brown formulated the question :

I once bought a radio clock, just to tap into it for the pulse - it was a matter of bypassing the circuit which limited it to receiving MSF for synchronisation once per 24 hours.

At a local universities radio rally junk sale, I came very close to buying a Cesium time clock in the early 1970's. It was only the thoughts of trying to explain the purchase to SWMBO which stopped lol

[Harry Bloomfield]

tim..... formulated the question :

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There is no guarantee that your radio clock is accurate, the best you can say is that - if it manages to receive a correction, when it is due once per 24 hour period, it should be accurate for that instant. After that instant it will drift + or - based upon the accuracy of its internal crystal.

[Harry Bloomfield]

Mike Barnes explained :

That is because Windows syncs itself by default once per day at a set time of day. If your PC is not turned on at that time, it will not sync itself, so it then has to rely upon its internal (not very accurate) RTC.

You can download a free utility which allows you to set how often (how many minutes) Windows should attempt to sync itself, from every few minutes to once per day. Mine is set to sync itself every 30 minutes and always agrees with my radio controlled watch.

[Nick Odell]

I was under the impression that under normal circumstances the chimes are broadcast live from the tower and when there is a malfunction they replace it with the pips, not a recording. Something I heard recently suggested that it was only during war-time that the live sound of the chime was replaced by a recording because the sounds of bombs and anti-aircraft fire etc would worry the nation.

Nick

[charles]

when I was working on a New Year's Eve at TC in the '60s, there was a model of Big Ben in Pres A and the 12 O'Clock rings were cued up on the tape deck in case the live Church Service on BBC1 overran. The year I was there it ddin't overrun, so the real thing was used.

[Ramsman]

My watch (Citizen Eco-Drive) and clocks receive their signals from the German transmitter at Mainflingen near Frankfurt am Main. I haven't checked them against any GPS devices, but I shall do so.

I noticed during the BBC Olympic broadcasts that the stadium clock was about seven seconds behind my watch.

[Harry Bloomfield]

on 21/08/2012, Nick Odell supposed :

I was told by a BBC colleague several years ago that they then used a recording. The reason he said was due to unpredictable traffic noise, possible 999 sirens and rumble in the back ground.

[Andy Burns]

If you were in the stadium I expect the clock would have agreed with your watch, most of the the delay if watching on digital TV will come from compressing it before transmission and decompressing it after receiving to display the picture.

[The Natural Philosopher]

That's about the video delay on a typical digital TV receiver. Oddly enough the delay difference between the TV in the kitchen - a sony digibox/analogue and the DTB card in my computer is enough that I can get the coffee upstairs to the office without missing anything at all.

Anyway thank god for linux, which simply installs ntp and gets on with syncing from half a dozen time servers out of about 150 listed, somewhere in the world.

[Harry Bloomfield]

I would not expect the stadium clock to be out, I wonder if there might have been a deliberate delay loop in the transmission? There is always some delay in digital broadcasts, then more delays inside the TV set decoding it. Overall, a second or so.

My radio watch attempts a sync once per 24 hours. If it fails on the first attempt to get a sync, it tries a second time an hour later. If successful it shows a little satellite (?) symbol in its LCD display. Amazingly, I have never known it fail to manage to gain sync in the 7 years I have worn it - thinking back to when I built a large specialised MSF receiver and how I struggled to get stable reception. lol

[Dave Liquorice]

Agreed but it's pretty good for clockwork.

No I don't think so, live mics from up the tower.

Yes digits make most things "non-live" these days. Watching our "live" limpic footy off DSAT when in the ground had about a 5 to 6 second delay. Menat you could be doing something else but not miss anything. B-)

Several thousand, picking for your locality from

is a good starting point. AFAIK Windows only allows one server to be polled, linux allows many and compenstates for the circuit delays and differences in the results from each server.

The timing of the pulses is accurate as well not just the full minute.

The slow code is still there but fairly sure the fast code has been dropped as nothing used it. Yep:

[Dave Liquorice]

No just the cumulative effect of all the delays in a modern digital broadcast systems. See my other post, I made it about 5 seconds between directly viewed venue action and seeing the same action come back down via DSAT.

[Harry Bloomfield]

DSAT delays do seem much longer than Freeview ones, even allowing for the transmission distance.

[Tim Watts]

I'm having a vision of 2 workmen up there at an inopportune time with a copy of the Sun:

"Wooor, look at the..."

[Tim Watts]

And if you install a proper NTP client, it will try to maintain a drift correction factor between NTP time and the local (kernel software) clock which improves accuracy between NTP remote queries.