Horloge Ronde Shi's radio room clock.

Shi's radio room clock. Wikipedia: tous les postes using 2182 kHz font appel à la required to maintain a strictly enforced three-minute silence and listening period twice each hour, starting at h+00, h+30. This allowed any station with distress, urgent or safety traffic the meilleure chance of being heard at that time, even if they were at some distance from from other station, operating on reduced battery or perhaps reduced antenna efficiency, as for examfrom a dismasted vessel. As a visual aide-memoire, a typical clock in a ship's radio room would have these silence periods marked by shading the sectors from h+00 to h+03 and from h+30 to h+33 in green. Similar sectors e marked in red for what used to be the corresponding silence and listening period on 500 kHz between h+15 and h+18 and from h+45 to h+48.[4] These silence periods are no longer required as the introduction of GMDSS producedees autre automc watchkeeping systems et la bande de 500 kHz is no longer in use for maritime traffic.