Chelsea Radio Room Clock, circa 1950.
In 1927 at the International Radiotelegraph Conference held in Washington DC, the following standards for maritime distress calls was established:
§ 21. The automatic alarm signal must fulfil [sic] the following conditions :
The signal must be capable of being sent by hand or by automatic apparatus, without difficulty and with a precision in timing which must not be greater than can be judged from a watch or a clock having a seconds hand.
(b) Its composition must be clear, distinct, and easily recognized by a person ignorant of the Morse Code; and it must lend itself to the easy and cheap construction of an automatic receiver which:
1. responds. to the alarm signal even when many stations are working and when there is atmospheric interference;
2. is not actuated by strong signals or by atmospherics when these are not accompanied by the alarm signal;
3. possesses a sensitiveness equal to that of a receiver with a crystal detector connected with the same aerial;
4. gives warning when its operation ceases to be normal.
(c) The signal must be different from the signal used for the adjustment and working of the variometer.
…
(e) The following alarm signal is henceforth recognized : a series of twelve dashes sent in one minute, the duration of each dash being four seconds and the duration of the space between two, dashes, one second.
(f) This special signal must have for its sole purpose the actuation of the devices used to give the alarm. It must be used solely to announce that the distress signal is about to follow.
(g) The adoption of the type of alarm signal mentioned in (e) does not prevent an Administration from authorizing. the use of an automatic apparatus which would comply with the conditions fixed above and would be operated by the regulation distress signal (…———…).
The Chelsea Clock Company developed a clock to fulfill these conditions.
Most maritime radio traffic was conducted on the 600 meter band. The triangular red areas on the dial face indicated the two weak signal listening periods: 15 – 18 minutes after the hour and 15 – 12 minutes before the hour. During these times routine radio traffic was prohibited to allow for weak signal distress calls.
The red strips on the outer edge of the clock mark the twelve four second on periods and the space indicates the one second off periods. Required by the new standards. These transmissions would have set off an automatic alarm in the radio room of nearby ships to alert the operator that a distress call was about to follow.
Note also the short third hand which could be set to show the time at the home port or GMT.
Now all I need to do is mount it on a nice wood backing to hang on the wall in my shack.
