Editing Time signal (section)

===Dedicated time signal broadcasts===
The telegraphic distribution of time signals was made obsolete by the use of AM, FM, [[shortwave radio]], Internet [[Network Time Protocol]] [[Server (computing)|servers]] as well as [[atomic clock]]s in [[Satellite Navigation|satellite navigation]] systems. Time signals have been transmitted by radio since 1905.<ref name=Burns04>{{cite book | first=R.W. | last=Burns | title=Communications: An international history of the formative years | publisher=IET | year=2004 | isbn=0863413277 | page=121 }}</ref> There are dedicated [[Radio clock#List of radio time signal stations|radio time signal stations]] around the world.

Time stations operating in the [[longwave]] radio band have highly predictable [[radio propagation]] characteristics, which gives low uncertainty in the received time signals. Stations operating in the [[shortwave]] band can cover wider areas with relatively low-power transmitters, but the varying distance that the signal travels increases the uncertainty of the time signal on a scale of milliseconds.<ref name=McCarthy-Seidelmann-2009>{{cite book |first1=Dennis D. |last1=McCarthy |first2=P. Kenneth |last2=Seidelmann |year=2009 |title=Time: From Earth rotation to atomic physics |publisher=Wiley-VCH |isbn=978-3-527-40780-4 |page=256}}</ref>

Radio time signal stations broadcast the time in both audible and machine-readable [[time code]] form that can be used as references for [[radio clock]]s and [[Watch#Electronic|radio-controlled watches]]. Typically, they use a national or regional [[longwave]] digital signal; for example, station [[WWVB]] in the U.S.&nbsp;.<ref name=McCarthy-Seidelmann-2009/>

The audio portions of the shortwave [[WWV (radio station)|WWV]] and [[WWVH]] broadcasts can also be heard by telephone. The time announcements are normally delayed by less than 30&nbsp;ms when using land lines from within the continental United States, and the stability (delay variation) is generally {{nobr|less than 1 ms.}} However, when [[mobile phones]] are used, the delays are often more than 100&nbsp;ms, due to the multiple access methods used to share cell channels. In rare instances when the telephone connection is made by satellite, the time is delayed by 250–500&nbsp;ms.

The audio from the broadcasts is available by telephone by dialling U.S. numbers {{nobr|(303) 499-7111}} for [[WWV (radio station)|WWV]] (Colorado), and {{nobr|(808) 335-4363}} for [[WWVH]] (Hawaii). Calls (which are ''not'' toll-free) are disconnected after 2&nbsp;minutes.
[[File:Low cost DCF77 receiver.jpg|thumb|A low cost [[Low frequency|LF]] [[radio clock]] receiver, antenna left, receiver right.]]

[[Loran-C]] time signals formerly were also used for radio clock synchronization, by augmenting their highly accurate frequency transmissions with external measurements of the offsets of LORAN navigation signals against time standards.