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Old 26-08-2008, 19:23   #16
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.......The Cospas/Sarsat specification requires that EPIRBs be designed to prevent inadvertent activation and a further protection is required in that the specification also requires that the distress alert must not be transmitted by the beacon until at least one transmit repeat cycle has elapsed (a cycle is 50 secs so after activation the second burst is at approx 100seconds). ......
Midland, if I may (and please take no offence as I am just being pedantic here), I understand that the first transmission (coded as inactive) occurs at switch on so the second (active) transmission occurs between 50 and 60 secs after switch on rather than 100 seconds.
That said, I appreciate the depth of information in your post (both this thread and others), I find them very imformative.
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Old 26-08-2008, 20:16   #17
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Midland, if I may (and please take no offence as I am just being pedantic here), I understand that the first transmission (coded as inactive) occurs at switch on so the second (active) transmission occurs between 50 and 60 secs after switch on rather than 100 seconds.
Yes I agree Wotname, thanks for pointing it out.

I was not altogether clear when I first mention the cycles but got it clearer later when I refer to the distress message not being at least until 50 secs (approx) after activation. The "at least" because I believe that the specification does not make it mandatory that the distress message has to be in the second (ie zero + approx 50 sec burst) just that it cannot be earlier - I don't know what the manufacturers' practice is with that though.

I refer back to that second mention of 50 secs by me because I went on to say that for the distress message to be sent the EPIRB had to be in the water during that time if it was water activated - on reflection that might be an assumption of mine. I have always assumed that the delay in sending the distress message was to provide a temporal guard against accidental initiations of the distress message from fleeting manual or water activated switch ons (ie assisting in meeting the specified requirement for designed in protections against accidental initiation of an alert), but I have no authoritative reason to claim that.

In case some others are wondering about the reference to my "approx 50 seconds" for the tx cycle the cycle is randomised among EPIRBs (between forty something seconds and fifty something seconds - stated more exactly than that in the spec though ) in order to reduce the probability of 2 activated EPIRBs transmitting their distress messages on top of each other and so interfering.

Harking back to your earlier post Wotname where you mention the cold start time for GPS type EPIRBs, do you have any knowledge as to how long this typically is in practice?

John
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Old 26-08-2008, 23:12   #18
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Originally Posted by hellosailor View Post
Many EPIRBs that appear to only be manually activated, are also WATER ACTIVATED if salt water manages to get across two of the casing screws. This is an intentional feature that may be totally invisible to the owner. A little water gets to the EPIRB, or it gets stored and splashed on deck, and voila, another false alarm overloading the SAR system.

I've seen ACR EPIRBs with this design flaw, and I call it a flaw because it should be molded or labelled on the case, so it can't be missed.
Hi Hellosailor

This is not a response designed to condradict or challenge you - I think it is clear that I have a genuine interest in EPIRB operation .

I am now on our boat for a couple of days and so have pulled out my own EPIRB to see what it says on its case label. The first statement is quite clear on the matter - "Once separated from bracket EPIRB will activate via water sensor". It is an ACR, quite old now as was serialised in 1996 (next battery/service in 2011 so will be junked by ACR then under their aging policy).

Further on it says "To stop transmission remove EPIRB from water". I think this maybe confirms my assumption mentioned in my last post that this EPIRB, at least, will not operate if splashed - it would seem that if it is activated in water it needs to be in the water for the approx 50 secs before it will transmit a distress alert as if the contacts are not wetted between them for this time the tx will stop (my EPIRB appears to use two case screws for the contacts as you mention).

I don't know what is on other EPIRBs, including other ACR ones, as I know how they work and never read the label (not sure if that warrants a or a ).

Could you advise what ones you have seen without a notice regarding in water operation?

John
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Old 29-08-2008, 02:52   #19
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....
Harking back to your earlier post Wotname where you mention the cold start time for GPS type EPIRBs, do you have any knowledge as to how long this typically is in practice?

John
Opps... forgot all about this question, must be using too much solvent in the refit .

I haven't had the need (opportunity?) to test a EPIRB / PLB with an embedded GPS yet so can't give a definitive answer; however I can say that most GPS engines are pretty much the same these days especially in the lower end of the market.

Therefore I would expect the GPS receiver in the average EPIRB / PLB would be much the same as the GPS receiver in cheap hand held GPS units. Most of these will cold start and self locate within 10 minutes. Even the GPS receiver in my CHEAP chinese made mobile phone (cell phone) will provide a position in 5 minutes or so from a cold start.
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Old 29-08-2008, 03:04   #20
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Thanks for the feedback on that Wotname.

Was thinking that if they tended to stray out to 10 minutes it starts knocking off quite a big proportion of the fix time advantage held by the GPS ones over those reliant on an orbiting satellite doppler fix.

John
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Old 29-08-2008, 04:35   #21
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Hmm... hadn't really thought about the time advantage between the GPS / non GPS beacons; never thought beyond the accuracy advantage of the GPS augmented beacons.

This must be why I like CF.
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Old 14-01-2009, 03:28   #22
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Hi

Is there any objections for a European to by an US EPIRP, are there any difrences, can i register as well on the nooa site or do i need to ba US?

Best regards
Lagoon
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Old 14-01-2009, 12:10   #23
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Lagoon-
Contact NOAA directly by email at sarsat.webmaster@noaa.gov to get a definitive answer. You probably can get away with this, but I'd suggest checking with the authorities wherever your vessel is flagged to make sure you aren't also violating their rules.
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Old 14-01-2009, 12:20   #24
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SARSAT: Types of EPIRB

http://www.sarsat.noaa.gov/emerbcns.html
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Old 14-01-2009, 12:26   #25
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My personal preference is for the auto activate in water ones as it means I can (actually "could", as it has never happened yet ) tie the lanyard to myself or the raft and the thing would start automatically in the water without having to worry about my breaking protective tabs, etc to get the thing going. But each to their own, as long as they understand what they are getting or not getting for their money.
My understanding is that a water-activated EPIRB will only activate by itself at a depth of around 4m - hope you don't go that deep!

Roger
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Old 14-01-2009, 12:31   #26
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PHase out of 120s

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Beware of the 121.5/243 MHz epirbs flooding the second hand market lately , as of Feb 1 2009 these will no longer be monitored . The 406MHz signal allows a satellite local user terminal to accurately locate the EPIRB (much more accurately -- 2 to 5 km vice 25 km -- than 121.5/243 MHz devices), and identify the vessel (the signal is encoded with the vessel's identity) anywhere in the world (there is no range limitation).

Don't waste money on the 121.5/243 MHz (IMO)
Absolutely!!

"February 1, 2009: The Phaseout of 121.5 MHz Beacons for Satellite Distress Alerting
In October 2000 the International Cospas-Sarsat Program, announced at its 25th Council Session held in London, UK that it plans to terminate satellite processing of distress signals from 121.5 and 243 MHz emergency beacons on February 1, 2009. All mariners, aviators, and individuals using emergency beacons on those frequencies will need to switch to those operating on the newer, more reliable, digital
406 MHz frequency if they want to be detected by satellites.

The decision to stop satellite processing of 121.5 / 243 MHz signals is due to problems in this frequency band which inundate search and rescue authorities with poor accuracy and numerous false alerts, adversely impacting the effectiveness of lifesaving services. Although the 406 MHz beacons cost more at the moment, they provide search and rescue agencies with more reliable and complete information to do their job more efficiently and effectively. The Cospas-Sarsat Program made the decision to terminate 121.5/243 MHz satellite alerting services, in part, in response to guidance from the International Maritime Organization (IMO) and the International Civil Aviation Organization (ICAO). These two agencies of the United Nations are responsible for regulating the safety on international transits of ships and aircraft, respectively, and handling international standards and plans for maritime and aviation search and rescue. More than 180 nations are members of IMO and ICAO.

NOAA, along with the U.S. Coast Guard, U.S. Air Force, and NASA (the four Federal Agencies who manage, operate, and use the SARSAT system) are strongly advising users of 121.5/243 MHz beacons to make the switch to 406. Meanwhile, anyone planning to buy a new distress beacon may wish to take the Cospas-Sarsat decision into account."

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Old 14-01-2009, 12:55   #27
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"My understanding is that a water-activated EPIRB will only activate by itself at a depth of around 4m"
Nope. Got one, an older ACR, that activates if there is continuity (i.e. a salt water film) between two of the "cover screws" that hold the casing together. No pressure or depth sensor, all it looks for is continuity between the two screws.
In really clean fresh water, that means it probabaly would not trigger at all. In salt water...a good salt mist might trigger it. Which is probbaly part of the reason for, what is it, a 90% false signal rate?
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Old 14-01-2009, 14:42   #28
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My understanding is that a water-activated EPIRB will only activate by itself at a depth of around 4m - hope you don't go that deep!
You are getting confused between the automatic release of CAT I EPIRB's (the so called "Float Free" ones) and the automatic switching on of most EPIRBs when placed in water - Hellosailor has correctly described that function.

Obviously the float free ones automatically turn themselves on when they get in water but that is an entirely separate function to the automatic release of the EPIRB from its holder at around 4 m depth. In fact float free EPIRBs are generally just the exact same EPIRBs as a non float free one but just held into its holder by a water activated automatic release mechanism. Most, but not all, manually released EPIRBs also turn themselves on when placed in water using the same functionality for that as the float free ones do.

It is quite apparent that this need to be manually turned on limitation of some of the cheaper EPIRBs is not well understood but I note here in my country the resellers are now generally referring to the non automatic switch on ones as "manually activated" but in my mind there is still room for confusion with the float free EPIRBs.
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