Auto Alarms Responding to SOS ... (?) - Ships Nostalgia
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Auto Alarms Responding to SOS ... (?)

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  #1  
Old 27th April 2012, 07:52
Worldspan Worldspan is offline
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Auto Alarms Responding to SOS ... (?)

Back in the 1950s, someone once told me that there were auto alarms which were activated by the signal SOS. Is this true or were the only alarms those which we all knew ... and the circuit diagrams of which we had to learn by heart?

W
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  #2  
Old 27th April 2012, 08:07
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To the very best of my knowledge there were no auto alarms that could respond to the letters SOS. They had to be triggered by the 4 second dashes with one second intervals or as we all experienced 4 second bursts of QRN with one second intervals.
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Old 27th April 2012, 09:41
CrazySparks CrazySparks is offline  
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I'm with Tony Selman on this one - never heard of such a device - not from old time college lecturers or old R/O's at sea. Just imagine what QRN could do with those one second dots! Offhand
On a technical level, I'd say that the probability of ...---... appearing out of noise is very high. With either carrier detection or modulation detection, the time required to detect a dit would certainly be too long to differentiate a genuine signal from noise, so the '...' is a non-starter. The _ _ _ will also pop up very frequently. I think the false alarms would have driven an RO insane!
Modern digital radio systems use opening signal sequences that have very low probabilities of arising in noise, and which are mathematically very well defined. They have a property termed 'low cross-correlation' with noise - which means they don't readily appear in noise, and also good 'auto correlation' which means that if you compare the receiver output with a copy of the signal you want, you can have a defined confidence in correctly detecting the signal. This is quite a complicated field and I won't harp on here. Look up Barker Codes for further insights.
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  #4  
Old 28th April 2012, 00:59
rusty1946 rusty1946 is offline  
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As far as I know Marconi Marine made autoalarms in the 1950's dont know what triggered them whether it was the dashes of the opening sequencies or not
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  #5  
Old 28th April 2012, 01:12
trotterdotpom trotterdotpom is offline  
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The Seaguard, a boxful of cams and pawls, responded to the 4 second dashes, the same as the later electronic auto alarms.

John T
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  #6  
Old 28th April 2012, 12:40
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Quote:
Originally Posted by Tony Selman View Post
To the very best of my knowledge there were no auto alarms that could respond to the letters SOS. They had to be triggered by the 4 second dashes with one second intervals or as we all experienced 4 second bursts of QRN with one second intervals.
Makes me wonder how they initially determined the number of dashes to trigger the alarm. I'd have thought an additional dash would have markedly decreased false alarms due to QRN
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  #7  
Old 28th April 2012, 13:08
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Quote:
Originally Posted by mikeg View Post
Makes me wonder how they initially determined the number of dashes to trigger the alarm. I'd have thought an additional dash would have markedly decreased false alarms due to QRN
You are right, Mike, but increasing the number of required dashes would have increased the possibility of interference causing the resetting of the count and therefore the likelihood of missing a genuine alert. The whole thing was a mass of compromises and the design of the testing equipment was far more difficult and demanding than the design of the auto alarm itself. You not only had to design the dash generator, you had to be able to vary and set the max/min timings for dashes and spaces and to be able to generate and introduce various levels and types of interference. A nightmare at type-approval testing time, since all this had to be done with the equipment being cycled through the various climatic and environmental conditions.

When all that was over, the equipment was then taken down to St. Margaret's bay, installed in the terminal building for the cross-Channel telephone cable and connected to an antenna. There it was connected to a tape recorder with a loop facility that was able to record 2 (IIRC) minutes of the receiver audio output, 1 minute either side of the alarm being activated. It was left there for one month and the activations were logged. After each alert was received/activated, the equipment was reset and put back on watch and the audio loop was transferred to a reel-to-reel tape. The overall results obtained were later compared with the 500 kHz log of GNF.

During the on-air testing, I used to drive down once a week to meet Willie Horwood or John Proctor of the PMG T/A department and review progress of the "Lifeguard N" (and some years later the "Lifeguard II"). The comparison count was always in favour of the A/A equipment - it recorded many genuine alerts that GNF did not. None of them were in the Channel I hasten to add, they ones that GNF missed were all in the Baltic or Western Mediterranean.

Still it was reassuring that we never missed any genuine alerts. Better that than sacrificing alerts for the sole purpose of cutting back on false alerts from static. It was a nuisance to be roused from slumber in the tropics by a false alert, but nobody died as a consequence.
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Last edited by Ron Stringer; 28th April 2012 at 15:46..
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  #8  
Old 28th April 2012, 19:53
sparks69 sparks69 is offline  
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They had an Auto Alarm on all the time at the RAF Station (callsign MEX) on Gan Island.
Not sure what use it would have been considering the QRN would almost be QRN5 all night. My memories were that they were next to useless once the static crashes & bangs got going.
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  #9  
Old 28th April 2012, 21:06
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Originally Posted by R651400 View Post
I don't get the reasoning behind this comparison. All British coast stations had a finite area of distress responsibility and apart from maintaining the usual silence on 500 kc/s it's highly unlikely that GNF would be interested in any distress in the areas mentioned. I would however expect a ship's auto alarm to activate at such distances and even further.
The GPO recognised the difficulty of producing a laboratory test regime that could be confidently claimed to completely simulate the conditions existing on 500 kHz in all areas of the world. Although they appreciated the safety-critical nature of the A/A, the GPO's technical management were unwilling to have their test engineers spend weeks sailing around the tropics or other difficult receiving areas, in an effort to prove that such equipment would operate reliably in service. So, having subjected the equipment to all the laboratory tests that they had developed over the previous 30 or 40 years, they applied a belt-and-braces approach by putting the equipment under supervision in as near similar conditions as they could. That is, in a permanently-manned station close to the sea (about 20 metres from the high-water line) and in a 500 kHz high traffic zone (Dover Straits). There, over a period of 4 weeks, its performance in receiving alarm signals on 500 kHz was checked (as a performance control) against the 500 kHz logs at the nearest coast station some 40 km to the North of the test station at St Margaret's Bay (at the foot of the cliffs near Dover).

Radio regulations required the recording in the Radio Logbook of all ship radiotelegraph stations, the salient details (time, frequency etc.) of all alarm and distress signals received. There was no mention of recording only nearby signals. Having spent some years at sea, I had expected that the same obligation would apply to coast station radio operators and was surprised that the A/A, with its virtually sea-level location under the cliffs, using only a simple antenna and a TRF receiver, was able to detect, record and activate alarms from transmissions that were not recorded at the coast station. The latter had much more sophisticated receivers and more extensive antenna systems.

Maybe I ought not to have been so surprised, given the identity of the station chosen as the control.

ps The GPO test engineers were not at all surprised and were highly amused at my na´vetÚ.
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  #10  
Old 28th April 2012, 22:28
trotterdotpom trotterdotpom is offline  
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Ooooooh! Anyone here who owns up to working at GNF? Over.

John T
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  #11  
Old 28th April 2012, 23:01
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The Lifeguard N made a great watchkeeping receiver, especially with the BFO.
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  #12  
Old 29th April 2012, 05:57
Naytikos Naytikos is offline  
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I once had an SAIT auto-alarm (which I'm sure Ron will tell us was really made by someone else) which false-triggered several times a day static or not. It took a month before I found the cause to be a leaky coupling capacitor at the aerial input.
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  #13  
Old 29th April 2012, 09:46
Graham P Powell Graham P Powell is offline  
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Being a heavy sleeper, I had the 2nd mate come down from the bridge one night to wake me up as the auto alarm bell was ringing just above my head and
I hadn't heard it.....
I found whenever it went off that the distress or whatever was hundreds of miles away.
rgds
Graham Powell
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  #14  
Old 29th April 2012, 12:05
trotterdotpom trotterdotpom is offline  
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Quote:
Originally Posted by Naytikos View Post
I once had an SAIT auto-alarm (which I'm sure Ron will tell us was really made by someone else) which false-triggered several times a day static or not. It took a month before I found the cause to be a leaky coupling capacitor at the aerial input.
Water in the auto alarm will do that.

John T
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  #15  
Old 29th April 2012, 12:53
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I recall it was the 13th of the month when the AA went off at night due QRN, approx 02:00 & again 04:30 local got back to cabin for Zzz at approx 04:45 followed by ring from the bridge - fault on radar. All part of seagoing life
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Old 29th April 2012, 22:18
holland25 holland25 is offline  
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Possibly one of the upsides of being a Blue Funnel 2R/O. The 1st R/O's cabin was next to the Radio Room, mine was on the main deck outside the saloon. I never had a broken night because of false AA triggers.
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  #17  
Old 30th April 2012, 19:59
Naytikos Naytikos is offline  
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John T:
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  #18  
Old 1st May 2012, 03:02
alex page alex page is offline  
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The Marconi Vigilant required a 3 dash sequence to trigger it. The simple TRF receiver worked amazingly well, static was a problem but minor considering its basic design. I have often received northsea alarm signals in the central med.One thing I could never understand was having to learn and draw all the circuits and cam operation for your ticket, when you had a manual.Teaching the use of the manuals would have been more productive.

Rgds A
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  #19  
Old 7th May 2012, 19:13
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I always thought they were designed to respond only to static crashes.....
Chas
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  #20  
Old 7th May 2012, 21:16
sparks69 sparks69 is offline  
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A B E H D C S - the names of the relays in (I think) the MIMCO Seaguard autoalarm I can't repeat the mnomemic which I made up to memorise the workings of the thing it would be censored !
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  #21  
Old 8th May 2012, 15:00
Klaatu83 Klaatu83 is offline  
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The Auto Alarm was one of the things that came out of the titanic disaster. It did not respond to "S-O-S", but, as Tony Selman wrote, to a specific series of 4-second dashes and one-second intervals, transmitted (I believe) on 500 khz. The actual alarm was required to sound in the radio shack, the Radio Officer's stateroom, and on the bridge. The idea was that, in the event that it went off when the Radio Officer was off duty, or asleep, then he would be able to hear it in his stateroom; and even if he was absent from his stateroom (at mealtimes, for example), then the Bridge watch would hear it, and be able to contact him. The Auto Alarm was finally abolished in February 1999, when the new GMDSS communications came into effect, and many ships ceased to carry Radio Officers at all anymore.
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Old 8th May 2012, 18:17
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[QUOTE=Klaatu83;595542]The Auto Alarm was one of the things that came out of the titanic disaster. It did not respond to "S-O-S", but, ...

I am sure that automation was being dreamed up but the Merchant Shiiping (Wrieless Telegraphy) Rules 1920, "ships of class II .... are required to carry, in addition to a certificated operator, one watcher if the voyage exceeds eight hours but does not exceed 48 hours from port to port and two watchers if the voyage exceeds 48 hours from port to port".

Watchers had to show they were able to receive and understand the RadioTelegraph Dsitress signal and the Safety Signal also that he could determine if the receiver was operating properly. Successfully examined candidates received a Certificate in Proficiency as a Watcher in Radiotelegraphy.

Note that no mention is made of the Urgency signal. I wonder if that existed then?

(From M Notice no. 17 as revised October 1924).

As usual, once two extra wages (or bonuses anyway) were added to the opcosts there would have been pressure to find some automatic alternative.
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Old 8th May 2012, 20:02
trotterdotpom trotterdotpom is offline  
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Varley, I found a website called "The Telegraph Office" which says the Urgency Signal XXX (and the Safety Signal TTT) was in use at the same time as CQD, so it must have started in the early 1900s at least.

Just occurred to me that sending an Urgency message by Aldis lamp could be the origin of the expression "A flash in the PAN".

John T
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  #24  
Old 8th May 2012, 20:05
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Quote:
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As usual, once two extra wages (or bonuses anyway) were added to the opcosts there would have been pressure to find some automatic alternative.
Nothing changed - hence the GMDSS some 70 years later.
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  #25  
Old 9th May 2012, 00:39
hughesy hughesy is offline  
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did'nt you have to log an A/A test before going off watch??

all the best
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