15 giugno 2008

SOS, un secolo di allarmi

L'SOS sta per compiere cent'anni. Il codice internazionale per le chiamate di soccorso, entrato a far parte della storia e della memoria collettiva di tutti noi, utilizzato persino nelle canzonette, è stato ratificato nel 1906 nel corso della prima conferenza di Berlino, che destinò la frequenza dei 500 kHz al soccorso marittimo, ed entrò ufficiamente in vigore il primo luglio 1908.
Quello che quasi certamente il grande pubblico ignora è che la chiamata SOS era un'invenzione tedesca e che i telegrafisti venivano istruiti a trasmetterla non come tre lettere separate, ma come simbolo unico, senza interruzioni: ...---.... Prima di allora venivano utilizzate anche altre distress call, come CQD in Inghilterra o SSSDDD in Italia. E naturalmente la successione di punti e linee non ha alcun significato, il celebre Save our Souls lo hanno appiccicato dopo (anche se "sos" è la radice del verbo salvare in greco). Per un po' di storia della telegrafia vi raccomando Old wires and new waves, archiviato in versione testo su Internet e naturalmente The Victorian Internet di Tom Standage. Recentemente, Francesco Berio IK0UAG ha diffuso una presentazione PowerPoint intitolata La radiotelegrafia a 360°, una lezione che affronta la storia del telegrafo partendo dai Sumeri (giuro).
Per celebrare l'anniversario, Royal Mail ha emesso una serie di francobolli, cartoline e altri gadget dedicati al Search and Rescue at Sea (trovate tutto sullo online shop delle poste britanniche). La BBC ha invece preparato uno speciale che verrà diffuso il 18 giugno da The One show, sul primo canale televisivo di BBC ONE. Per l'occasione verranno mostrati il trasmettitore a scintilla della Lizard Wreless Station in Cornovaglia (l'unica sopravvissuta dall'epoca di Marconi) e un ricevitore e a coherer. Confido che qualcuno lo metta a disposizione di tutti su YouTube. Nell'attesa consoliamoci con questo articolo pubblicato dal newsmagazine del sito news.bbc.co.uk.

Save our SOS

By Finlo Rohrer
BBC News Magazine

It's 100 years since SOS came into force across the world as the standard signal for ships in distress. But times have changed in the rescue business.


Before the advent of radio if your ship got into trouble on some far off stretch of roiling sea, that trouble was not easy to get out of. Communication off the ship could only be achieved with other ships within distance, using either lights, flags or flares.
If you were in dense fog or in a howling gale far out at sea, and you started taking on water, the first communication most sailors would make was heaven-wards. At the tail end of the 19th Century, radio changed that. It's easy to forget today, but in the early days of radio there was no voice. If you wanted to say you were in trouble, if you wanted to say anything in fact, you had to do it through morse code. The code had been born after the advent of the telegraph and when the telegraph went "wireless" it continued in the new format. "In the early days when they were sending a radio signal there was no way of modulating. The only thing you could do was turn a transmitter on or off," says Carlos Eavis, amateur radio manager of the Radio Society of Great Britain.

Calling signals

Wireless telegraphy - or radio as we prefer to style it now - had its biggest early impact on maritime communication. Ships had been working out ways to communicate with other ships for centuries, but radio opened up the possibility of reliable communication with ships that were out of sight for the first time. And the most important of all calls that a ship's radio operator could make was a distress signal indicating the vessel was in danger of sinking.
But if your ship got into trouble on its Atlantic crossing in the early years of the 20th Century you wouldn't necessarily have signalled SOS. Before SOS there was CQD. The story is told in Karl Barslaag's 1935 book SOS to the Rescue. British radio operators on ships tended to have come straight from work on land-based telegraph and brought their signals with them. CQ was a general call to demand attention from all stations, preceding a time signal or other announcement. The Marconi company, the dominant power in early radio, suggested this signal be appended with a D to work as a distress signal. It didn't stand, as many have imagined, for "Come Quick Danger", merely indicating "attention, distress". But there was a problem. Dash-dot-dash-dot, dash-dash-dot-dash, dash-dot-dot was not the easiest combination to pick up. "It was too easy for someone to hear the C and the Q and not the D and ignore it completely and that happened on more than one occasion," says Mr Eavis.

Intense politics

At a conference in Berlin in 1906 the international wireless telegraphy community got together to try to agree something that would be both internationally acceptable, and impossible to mistake. The Italians were using SSSDDD, but it was the German suggestion of SOE - dot-dot-dot, dash-dash-dash, dot - that caught the imagination. But it was felt that it suffered from the same problem as CQD. The E, being one dot, could easily be missed.

THE CONTENDERS Marconi: CQD Italians: SSSDDD Germans: SOE/SOS

Eventually the conference plumped for - dot-dot-dot, dash-dash-dash, dot-dot-dot - a signal that is hard to mistake for anything else in the world of morse. "SOS is very simple you are not going to hear that at any other time," Mr Eavis says. But it needn't have been SOS of course. Being broadcast without a pause, the combination of dots and dashes could also have been read as IJS, SMB, or VTB. SOS won the day, coming into effect on 1 July 1908.
Since then it has stormed into popular culture, littered a thousand newspaper headlines and prompted numerous "backronyms". According to who you believed it was Save Our Souls, or Sinking Of Ship, or Send Out Succour or Save Our Ship. "None of which is correct," says Mr Eavis. "It doesn't stand for anything. It's simply non-stop, there are no spaces." It is believed the first ship to have sent out an SOS signal was the American steamer Arapahoe in 1909. When the Titanic was sinking in 1912, its operator first sent out CQD and then SOS, alternating. CQD persisted, particularly among British operators, for many years.

Standardising of rescue

But SOS was a landmark in global communication. In the intensely political world of early radio, the technological powers-that-be had been able to agree on something that would save lives, instead of going their own way. The 1906 conference in Germany was also a landmark for agreeing - against the vested interests of firms like Marconi - that communication should be possible between all stations using all systems.
And the legacy of the internationally co-ordinated attempt to save lives by standardising the way rescue was requested has been developed over the last century. But the humble SOS morse signal has lost its dominance. "The days of morse have long gone," says Humberside Coastguard watch manager Andrew Mahood. Instead, the Coastguard in the UK deal with half a dozen main avenues of distress call from on board vessels:

VHF radio call: Use channel 16 and start broadcast with "mayday, mayday, mayday". Then give details of identity, position and situation. Other users will keep channel clear and hasten to the location.
Digital selective calling: Automated button push system on many ships to indicate distress, allows inputting of reasons and automatically transmits position
Satellite phone call: Dial 999 or other emergency services number
Release of a beacon: Emergency beacon can be released which will broadcast position, other beacons automatically activate on contact with water
Mobile phone call: Call to 999, or the European-wide emergency number 112, or text message to someone who contacts Coastguard

Distress flare

But all hope is not lost for the SOS. Even Mr Mahood - who has not dealt with a morse SOS for eight years - concedes there are times when dot-dot-dot, dash-dash-dash, dot-dot-dot might be the only way.
"Morse still can be used if a person's on a boat and the radio's not working, then they will use the good old Mk I torch." It is certainly no more far-fetched than those who text for help. "We had a distress call from the Singapore straits," says Mr Mahood. "A woman texted her boyfriend who was in Yorkshire who sent us an e-mail we then got in touch with the Singaporean coastguard." And in Hardy Boys-style survival situations where you've crashed in the Andes and you need to improvise a transmitter, morse SOS will be your salvation.
But for the most part the art of morse communication and the heritage of the SOS, is carried on by the amateur radio community in Britain, the US and elsewhere, still scanning the airwaves.

[Quello che vedete qui sotto, invece, è l'immagine di un autentico "orologio del silenzio" installato nelle stazioni costiere. Quando la lancetta dei minuti entrava nei settori rossi, il marconista doveva mettersi all'ascolto di eventuali chiamate di soccorso. Il commento di Francesco, qui in calce, spiega questa procedura.]

2 commenti:

Francesco ha detto...

In tutte le stazioni radio marittime, sia di bordo che di terra ,vi era in posizione di buona visibilità per l’operatore , un orologio a parete. La sua particolare funzione non era quella di indicare semplicemente l’ora, bensì di visualizzare i “periodi di silenzio”. La procedura di soccorso prevedeva infatti che tutte le trasmissioni cessassero sulle frequenze di chiamata e soccorso per tre minuti ogni quarto d’ora, al fine di porre attenzione ad eventuali chiamate da parte di navi in gravissimo pericolo. In CW il silenzio radio era osservato a partire dai minuti 15 e 45 di ogni ora, in fonia ai minuti 0 e 30, tali settori erano evidenziati rispettivamente dai colori rosso e verde sul quadrante dell'orologio di stazione.Quando la lancetta dei minuti si poneva all’inizio di uno dei quattro quarti , il marconista con un colpo d’occhio capiva di dover interrompere le trasmissioni e ascoltare con attenzione la 2182 KHZ in fonia o la 500 Khz in CW. Queste frequenze erano affollatissime, poichè utilizzate dalle navi per chiamare le stazioni costiere. Una volta ottenuta una frequenza di lavoro,la nave si spostava e iniziava a trasmettere il traffico commerciale per l’armatore o la corrispondenza privata dell’equipaggio. La numerosa presenza di stazioni, rappresentava il cardine della sicurezza in mare, più operatori radio erano all’ascolto su di una medesima frequenza, più vi era la possibilità di ascoltare una chiamata di soccorso. All’inizio dei periodi di silenzio,come d’incanto tutte le trasmissioni s’interrompevano e la frenesia dei segnali da ogni dove, cedeva la priorità all’ascolto d’emergenza. Oggi sulla 500 non si ascolta più alcuna trasmissione del segnale di soccorso SOS poiché non è più utilizzata a tal fine. Per non cancellare cento anni di storia,in occasione della prossima conferenza mondiale delle radiocomunicazioni (WRC) verrà avanzata una proposta che faccia di questa frequenza, o porzione di banda, attorno a 500 KHz, una "Heritage Frequency" , una frequenza museo da usare per scopi commemorativi, dimostrativi e storici.

Andrea ha detto...

Francesco - che ringrazio - parla con cognizione di causa. Sa perferttamente che cosa significa lavorare in una stazione costiera. La proposta di istituire una frequenza museo è stata citata anche in questo mio post del 2006 (ormai la memoria storica di RP comincia a essere consistente). Spero proprio che le storie di Francesco diventino una sana abitudine.