DAB Radio clock timings

  Simsy 18:16 18 Jan 2008


I am well aware that the processes involved in digital radio mean that there may be a delay of a few seconds when listening to something "live", but how accurate would you expect the clock on a DAB radio to be?

It picks up the time that id transmitted as data with the DAB signal, and I would have thought that this should be fairly accurate, i.e. also within a few seconds.

I've, so far, been unable to find the actual spec for this.

My new DAB clock radio has varied by as much as 2 minutes from accurate! One day last week, after I set it manually, it was spot on at 7 in the morning with the "pips" on Radio 4. The next morning the clock was 2 minutes behind!!

I've spoken to the maker of the item who tell me that the unit "rounds" the time to the nearest minute. That strikes me as unlikely, but I'll take their word for it. They also said that the time on THE DAB signal can be up to a minute out. This strikes me as extremely unlikely, but before I go back to them and argue that something is wrong, I want to have my facts correct.

And in case anyone is thinking "weak signal", I have a signal strength of 1 bar below maximum, (constantly), and a signal quality of 95%-99%, (constantly).

So my question is;

"How accurate do you expect a clock on a DAB radio to be?"

Thanks in anticipation,



  oresome 19:25 18 Jan 2008

My expectation, which may well be removed from reality, is that the time synchronisation signal would be transmitted at 1 minute intervals, at which point the clock would update the minute and reset the seconds to zero.

How far removed the DAB time signal is from real time, I'm not sure, but would guess no more than a second or two.

The clock may free run when there is no radio signal and be more than a minute inaccurate when it next receives a signal especially if the radio is switched off for long periods.

Winning an argument with the manufacturer may depend on if they express an accuracy figure for the clock in the first place.

  Simsy 22:58 18 Jan 2008

Your explanation does make sense, but I suspect, it's not the case, and that the time data is more or less continuous, and accurate.

I'm really hoping someone can confirm this, or otherwise, with some certainty, and, hopefully, some provenence for it!

There are some other issue with the unit as well, and I suspect they are related and it's a duff unit!



  dms05 12:21 19 Jan 2008

Are you certain the Time is extracted from the DAB signal and not from RDS station ID? If it's the latter then the time could well depend upon the FM Station checking it's own RDS output.

  Simsy 12:32 19 Jan 2008

but yes, I am sure it's via the DAB signal. Ive seen that mentioned many times.

The thing is, I've another, different,very cheap make, of DAB clock radio, and that keeps perfect time. Even when they have both been depowered and repowered/reset, next to each other.



  puma22 20:52 20 Jan 2008

I have a pure DAB alarm clock. Often I wake up before the alarm goes off. I lay there and listen to the 7am new and then, the alarm which is set up to go off at 7am, chimes in after the headlines have been read. I've often wondered whether it is the BBC or whoever sends out the signal that has it wrong.

  Simsy 07:40 21 Jan 2008

someone at the BBC who was involved in creating the specs for DAB. Extracts of the response is below;


The DAB specification allows the time to be sent in two different formats, either HH:MM or HH:MM:SS.SSS. In HH:MM format, the time should change accurate to around one second, in HH:MM:SS.SSS format, it should be accurate to around 24ms, in both cases the point of accuracy being the point of transmission.

the accuracy on the BBC’s network is “only” +2secs. The time information is sent in the DAB transport stream approximately once per second, thus it is easy for a receiver to set its clock accurately to within a couple of seconds.


I've also got the following from the "Pure" website;


Why is the clock is showing the wrong time?

You may notice variations in the clocks displayed on PURE DAB radios. Variations in time can be attributed to many events such as encode time (at broadcast) and decode time (at the radio). You may even find multiplexes broadcasting slightly different times, so you will often see the clock shift when you move multiplexes. The radio looks at the time broadcast once every hour (from the moment it was first turned on), and makes any adjustments to the radio time at that point. For the other 59 minutes of the hour the radio runs a software clock independent of the broadcast. If the broadcast is not found on the hour check (e.g. the multiplex is off air), the radio will keep running its software clock until the multiplex reappears and once it reappears the radio will automatically change its clock to meet the clock broadcast time **to the nearest minute.** It's this adjustment of **to the nearest minute** which causes variations to be seen between different radios - even when listening to the same multiplex.

This isn't a fault with your radio and yes you may see variances in the time on different radios - but you should never see variances of more than a couple of minutes.


In fact my radio was 3 minutes out this morning!

I will be talking to Pure later.
Thanks for taking an interest.



  dms05 16:20 21 Jan 2008

Interesting reply from the Beeb. So it's long term accurate but may be short term inaccurate! It also suggests the software clock in your Pure DAB is pretty inaccurate at 15 minutes/week (12 hours per year). I suppose it depends upon when the DAB Radio actually synchronises with the Network. I assume the accurate time is continuously broadcast by the BBC and the actual radio synchronises at predtermined intervals. It would be interesting to leave the DAB running during the day and see how accurate it is compared to been turned off overnight. But their again it's not my DAB Radio!

  Confused-of-Kent 09:56 28 Jan 2009

My Logik LOGRC168D clock is losing time, but a lot more than just a couple of mins! It was fairly accurate last night at bedtime, but this morning when I woke up LATE at 7.04, the radio showed approx 6.20, meaning neither of the alarms had gone off!

Admittedly, it's not set to radio, as I tend to wake up to the CD alarm but this can't be the reason surely?

Any help would be appreciated, as I only bought the clock before Xmas and, having moved house, I can't find the receipt. I know it's here somewhere...

  laurie53 20:29 28 Jan 2009

Surely if your clock radio is not set to radio it won't be tuned to a DAB station so it won't be getting any DAB time information?

  Confused-of-Kent 16:17 29 Jan 2009

Wouldn't it do it automatically? If they make the thing with a CD player, it stands to reason it's not going to be set to radio all the time. I still don't understand how it managed to be 45 mins slow in the space of one night. Seems excessive

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