What time is it?
Discussion
In our house, we have ‘normal’ tv, dab radio, fm radio, internet tv, iPads, computers etc (get us).
As an example, of we have the analogue tv on in the kitchen, internet tv on in the living room, the signals don’t align - there is a gap (sometimes quite a large one of several seconds) in speech between the two.
Another example - the ‘pips’ on R4 occur at subtly different times between the analogue radio, the dab radio and streamed internet radio.
So why does this happen, and which is most accurate? I’m guessing the reason for analogue type stuff is tv/radio receiving from different transmitters, but we’ve even noticed a difference between analogue kitchen tv and living room tv when it is on an analogue signal, and I see no reason why 2x tv’s a few metres apart would pick up an analogue signal from 2 different transmitters.
I know it’s not a major problem from a domestic point of view, but it certainly would be from a ‘science’ point of view, even for relatively simple experiments etc.
Anyone?
As an example, of we have the analogue tv on in the kitchen, internet tv on in the living room, the signals don’t align - there is a gap (sometimes quite a large one of several seconds) in speech between the two.
Another example - the ‘pips’ on R4 occur at subtly different times between the analogue radio, the dab radio and streamed internet radio.
So why does this happen, and which is most accurate? I’m guessing the reason for analogue type stuff is tv/radio receiving from different transmitters, but we’ve even noticed a difference between analogue kitchen tv and living room tv when it is on an analogue signal, and I see no reason why 2x tv’s a few metres apart would pick up an analogue signal from 2 different transmitters.
I know it’s not a major problem from a domestic point of view, but it certainly would be from a ‘science’ point of view, even for relatively simple experiments etc.
Anyone?
There isn't any analogue TV anymore.
This is a good article covering the time lags for various broadcast stuff
https://www.radioandtelly.co.uk/timelag.html
This is a good article covering the time lags for various broadcast stuff
https://www.radioandtelly.co.uk/timelag.html
pocketspring said:
Because the signal has to be coded to digital which takes a couple seconds. If I'm watching HD upstairs and someone is watching analogue downstairs, I'll hear the speech a second before from the downstairs tv one.
If you're still able to watch UK analog TV, you must live on a planet round a star about 12 light years away... https://en.wikipedia.org/wiki/Digital_switchover_d...
Video is digital pretty much from the moment it's captured by a camera CCD to the point where it ends as a pixel on your TV screen. The conversion between analog and digital domains is not the reason for lag.
Lag on video happens because of all the processing that occurs in the digital domain. Processing, filtering and synchronization all add delays, but the biggest one is typically the compression process - taking the firehose of bits from the raw digital data and working out which ones to throw away to maximize the number of TV channels you can send to your expensive satellite or other digital uplink.
https://www.redsharknews.com/is-there-a-solution-t...
If you want really accurate time info, GPS-based clock is the way to go.
Or use the Rugby clock as it was known.
Now based in Cumbria.
I have a Oregon Scientific clock that is set to the signal.
https://en.m.wikipedia.org/wiki/Time_from_NPL_(MSF...
Now based in Cumbria.
I have a Oregon Scientific clock that is set to the signal.
https://en.m.wikipedia.org/wiki/Time_from_NPL_(MSF...
V8FGO said:
Or use the Rugby clock as it was known.
Now based in Cumbria.
I have a Oregon Scientific clock that is set to the signal.
https://en.m.wikipedia.org/wiki/Time_from_NPL_(MSF...
MSF clock is millisecond accurate, but there's no compensation for signal propagation. The further you are from the transmitter, the later the apparent time.Now based in Cumbria.
I have a Oregon Scientific clock that is set to the signal.
https://en.m.wikipedia.org/wiki/Time_from_NPL_(MSF...
GPS clock is accurate to ~30 nanoseconds regardless of your location.
I've used one of these for the last 30 years:
'The Junghans 'Mega' desktop clock receives a long-wave radio signal every day broadcast on 60 KHz (call-sign MSF) from Rugby, UK, carrying time information from Britain's national atomic clocks at the National Physical Laboratory, Teddington.'
https://www.rmg.co.uk/collections/objects/rmgc-obj...
Slightly surprised but honoured to find 'my' clock in the Royal Museum Greenwich!
'The Junghans 'Mega' desktop clock receives a long-wave radio signal every day broadcast on 60 KHz (call-sign MSF) from Rugby, UK, carrying time information from Britain's national atomic clocks at the National Physical Laboratory, Teddington.'
https://www.rmg.co.uk/collections/objects/rmgc-obj...
Slightly surprised but honoured to find 'my' clock in the Royal Museum Greenwich!
silentbrown said:
GPS clock is accurate to ~30 nanoseconds regardless of your location.
The Junghans website says 'more accurate than GPS and considerably more energy efficient'...Bottom section at https://www.junghans.de/en/service/faqs/
V8FGO said:
Now based in Cumbria.
Anthorn, just 3 miles from me! Apologies for the ‘analogue’ comment, but point remains - out of tv (internet), tv (free view, mea culpa), radio (fm), radio (dab), and just general internet connected device such as an iPad, and ignoring the need for absolute accuracy for experiments etc., which is the most ‘accurate’ (as opposed to ‘precise’)?Edit - accidentally jumped in before reading the very useful link provided above!
ChevronB19 said:
V8FGO said:
Now based in Cumbria.
Anthorn, just 3 miles from me! Apologies for the ‘analogue’ comment, but point remains - out of tv (internet), tv (free view, mea culpa), radio (fm), radio (dab), and just general internet connected device such as an iPad, and ignoring the need for absolute accuracy for experiments etc., which is the most ‘accurate’ (as opposed to ‘precise’)?Edit - accidentally jumped in before reading the very useful link provided above!
Simpo Two said:
The Junghans website says 'more accurate than GPS and considerably more energy efficient'...
Bottom section at https://www.junghans.de/en/service/faqs/
The accuracy claim is complete nonsense. Energy efficient is very true. Bottom section at https://www.junghans.de/en/service/faqs/
It is true that GPS time is a separate time scale which is not synchronised to UTC (the world standard for time). However, the deviation between GPS time and UTC is constantly monitored and embedded into the GPS signals, so that GPS receivers actually emit UTC time (unless configured not to).
GPS receivers are easily a factor of 100,000 more precise (30-100 ns) than a typical LW time signal receiver (3-10 ms); Accuracy in the ns range (i.e. small enough that aerial cable length is a major source of error), whereas the LW time signal needs to be corrected for location, and may have multiple ms of error within the UK otherwise.
As GPS signals are steered to always match UTC, there is no long-term deviation between the systems.
Edited by WatchfulEye on Tuesday 30th May 19:09
I have a couple of Linux servers running NTP (network time protocol) and I also have a clock that syncs to the aforementioned MSF time signal.
They all agree with each other amazingly.
On the other hand, we have a few other clocks that are always a few minutes out as well!
As for the TV & Radio signals and the delays between the various devices - there's quite a delay between R2 on FM, DAB and internet radio.
TV will vary between satellite, cable and freeview transmissions simply due to the mechanics involved in getting the signal from the point of origin to the various broadcasting services (same for radio).
They all agree with each other amazingly.
On the other hand, we have a few other clocks that are always a few minutes out as well!
As for the TV & Radio signals and the delays between the various devices - there's quite a delay between R2 on FM, DAB and internet radio.
TV will vary between satellite, cable and freeview transmissions simply due to the mechanics involved in getting the signal from the point of origin to the various broadcasting services (same for radio).
Encoding and decoding will inevitably create delays as well.
A lot of old public clocks in train stations, public buildings etc run off mains electricity and use the 50Hz frequency to maintain time. It is kept pretty accurate so works quite well.
A lot of old public clocks in train stations, public buildings etc run off mains electricity and use the 50Hz frequency to maintain time. It is kept pretty accurate so works quite well.
Edited by Beati Dogu on Tuesday 30th May 23:05
Gassing Station | Science! | Top of Page | What's New | My Stuff