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When did the Greenwich Time Signal get the long beep at the end and why?
It used to be six beeps of the same length but changed some time in the Seventies, I think.

How come?
asked in Greenwich Time Signal, radio, broadcasting

P-Kasso answers:

No idea when it changed but the reason why the last tone is longer is very logical.

The long last tone signifies that that is the PRECISE stroke of the hour - very exact although, paradoxically, latest developments in digital and satellite broadcasting (and the time lag) make this less accurate than i was a few decades ago.

Supplement from 05/17/2008 06:22pm:

Just swanned round Wiki which is very good on the early history of the pips but strangely silent on the seventh pip.

Wiki says (among other interesting things)

"The pips have been broadcast daily since 5 February 1924, and were the idea of the Astronomer Royal, Sir Frank Watson Dyson, and the head of the BBC, John Reith. The pips were originally controlled by two mechanical clocks located in the Royal Greenwich Observatory that had electrical contacts attached to their pendulums. Two clocks were used in case of a breakdown. These sent a signal each second to the BBC, which converted them to the audible oscillatory tone broadcast.

The tone on the line was inverted; that is to say, the signal sent to the BBC was "on" when no pip was required, and was pulsed "off" when a pip should be sounded. This allowed a fault on the line to be detected immediately."


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Aiming4777 answers:

You are right, the change was made in 1972. The BBC now keeps its own time with two atomic clocks sited in the basement of Broadcasting House. These are kept in step by signals received from the Global Positioning Satellite (GPS) system and by information received from the Rugby radio transmitter facility from the National Physical Laboratory.

The Greenwich Time Signal, or “Pips” as they are known, no longer gives Greenwich Mean Time. Since 1972, all the time signals in the world have been based on atomic time. This is far more regular than Greenwich Mean Time which drifts as the speed of the Earth's rotation changes. Differences between the two mean that "leap seconds" occasionally need to be added to the time signal, by means of an extra pip. This keeps the two types of time roughly in step.

This oddity is one of the reasons why the last pip is slightly longer than all the rest.

Source: http://news.bbc.co.uk/1/hi/sci/tech/271319.stm
You can hear the ‘pips’ from this link: http://greenwich2000.net/im/time/Gts_pips.wav

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