BBC Greenwich Time Signal inaccurate

Ainsley1

I am coming to this discussion at least a day late so my body clock must be very inaccurate :rotfl:

Yes as already posted atomic clocks are pretty accurate in terms of stability i.e. the clock frequency...But not necessarily the absolute time derived from them owing to processing and communication delays. Several systems can have that delay corrected and use many clocks together to improve accuracy even further. Now there are optical atomic clocks under development accurate in frequency to 1 second in billions of years!

There are specialist time readers that use the many signals transmitted from the GPS satellites resulting in absolute time accurate to better than a few microseconds. The GPS system is derived from atomic clocks. But the issue arises as to what we mean by accurate and I am not going into that on here! It really is all relative to what we want to use the time information for.

The transmitter at Rugby used to be one of the best available for accuracy of coded time but that is really (although their simple type is still very useful) old hat with the GPS system and the like.

If you want a good easily accessed time display on a computer (or synchronisation) provided you have a good download speed then the World Time Server that is derived from atomic clocks - if I remember correctly it used to be from NASA? - is useful SEE http://www.worldtimeserver.com/

I think the 'moral' of this thread is find a source that meets your needs. For most of use a few seconds is irrelevant.......And I often find periods with no clock watching particularly relaxing. Get up when it is light, eat when hungry, go to bed after the pub shuts and care not if 'time' is called late!!:T

John_Gray

Ainsley1 wrote: »

I think the 'moral' of this thread is find a source that meets your needs. For most of use a few seconds is irrelevant.......And I often find periods with no clock watching particularly relaxing. Get up when it is light, eat when hungry, go to bed after the pub shuts and care not if 'time' is called late!!:T

Unfortunately I don't think there is an MSE Forum which covers Philosophy!

unforeseen

Frozen_up_north wrote: »

The time signals from the BBC aren't broadcast with any degree of accuracy, as others mentioned there are delays due to digital processing which make the broadcast of pips hit and miss.

The timing of the BBC pips is designed such that they will be​ accurately received on long wave within 100 miles of the main UK AM transmitter at Droitwich. So the answer is that the pips on Radio 4 198khz are the most accurate

50Twuncle

Ainsley1 wrote: »

I am coming to this discussion at least a day late so my body clock must be very inaccurate :rotfl:

If you want a good easily accessed time display on a computer (or synchronisation) provided you have a good download speed then the World Time Server that is derived from atomic clocks - if I remember correctly it used to be from NASA? - is useful SEE http://www.worldtimeserver.com/

But why is the download speed important ?
I used to connect at perhaps 25kbps and still got the correct time via auto time update !!
I now connect at 70Mbps

RumRat

First world problems eh???

spud17

RumRat wrote: »

First world problems eh???

You do need an accurate time, else how are you going to be fashionably late?

fenlander_uk

RumRat wrote: »

First world problems eh???

You never know when a topic will hit the geek loud button.;)

System

Hi

Well my wristwatch is available to view, if it would help.

I can adjust it at will to account for satellite lag, A to D conversion, BST, BSE and whatever else you want. Even try and remove the second hand to avoid controversy.

Ainsley1

But why is the download speed important ?

Well uncle consider a hypthetical download speed so fast that it cannot be measured then the time to load the data bits from source to pc would be nearly instantaneous so high accuracy (ignoring other delays).
Opposite end of the spectrum one bit a day would tend to cause a bit of a delay......That could be quite important if there wasn't any correction done.

One way to overcome the time span to transmit and receive a coded time word is first to transmit a marker and then the coded time that refers to that marker. That then enables the time from marker to end of word to be measured and a correction added. Can be done in real time but also attached to records to enable events to be accurately measured on a record.

It is the not so subtle difference between transmitting a known accurate frequency (a clock frequency) and adding on to that clock, data that gives real time information? By the time the info is read and decoded time has moved on......And other posts intervene...:rotfl:

50Twuncle

Ainsley1 wrote: »

Well uncle consider a hypthetical download speed so fast that it cannot be measured then the time to load the data bits from source to pc would be nearly instantaneous so high accuracy (ignoring other delays).
Opposite end of the spectrum one bit a day would tend to cause a bit of a delay......That could be quite important if there wasn't any correction done.

One way to overcome the time span to transmit and receive a coded time word is first to transmit a marker and then the coded time that refers to that marker. That then enables the time from marker to end of word to be measured and a correction added. Can be done in real time but also attached to records to enable events to be accurately measured on a record.

It is the not so subtle difference between transmitting a known accurate frequency (a clock frequency) and adding on to that clock, data that gives real time information? By the time the info is read and decoded time has moved on......And other posts intervene...:rotfl:

But that is not "download speed" - that is LAG - ie) the time taken for the signal to arrive - which depends on carrier speed - not download speed !
The actual data itself will be a tiny amount - which will cross from the sender to the receiver in a fraction of a second - which is what I am trying to say - that the time taken to get the data from the sender to the receiver depends purely on the delay brought about within the receiver itself (the time taken "mid air" will be virtually zero (almost speed of light) )