BBC radio has been broadcasting the six-pip time signal since 5 February 1924, after setting up a joint venture with the Royal Observatory, Greenwich. The system connected Greenwich timekeeping technology with BBC broadcast technology.
From the start, the pips have proved accurate, reliable and extremely popular with an increasingly-time-bound global audience.
But a new technology being introduced to broadcast radio, digital audio broadcasting (DAB), has caused a problem with the accuracy of the time signal.
BBC radio is now broadcast not only for conventional analogue receivers, but also for digital radios, digital televisions and the internet. However, anyone listening on a digital set will have discovered a delay – of several seconds – which means that, whilst the analogue pips remain correct, the digital version cannot be used as an accurate time signal.
The broadcast delay on DAB, while substantial, is relatively predictable, meaning that a fix could be introduced at the transmitter end to broadcast 'early', causing the signal to be received 'on-time'. But a far bigger problem is an additional delay introduced by each radio receiver as it processes the signal.
Unfortunately, that delay varies from model to model – up to seven seconds in the worst case – and it is this receiver delay variation which prevents the BBC from implementing a standard solution. Internet listeners have an even greater problem, with delays being particularly unpredictable on that medium.
Technicians at the BBC have told us how they plan to address the issue. While the problem rests more with receivers than the transmitters, nevertheless they hope to introduce a solution which will fix the problem for 90% of sets (although no date has been given) which would yield pips accurate to about 0.2 seconds for those receivers. But those one-in-ten listeners with receivers outside the norm will not be able to use the pips as an accurate time signal.
[Please note: this article was last updated 2 June 2005]
Where else can one get accurate time-of-day? An alternative service is the MSF radio signal, a coded message broadcast from Anthorn in Cumbria which originates from the atomic clocks in the National Physical Laboratory, the UK's official timekeeper. Clocks and watches which set themselves right according to this radio signal are becoming cheaper and more common.
Alternatively, the British telephone time service, the Accurist 'speaking clock', remains a popular and convenient option as it has done since its inception as 'TIM' in 1936. But listeners to BBC radio who time their lives according to the familiar pips should note that the signal heard on all conventional analogue radios is still as accurate as ever.