Are EPIRBs dead?

[Wotname]

Originally Posted by transmitterdan

Here in the US I have not seen one of modern vintage without automatic water activation. I have been told that floating the unit in water is the best way to ensure the signal is maximized. I was told the antenna is designed for maximum radiation when it is just above the water. Whether this is true or not I cannot say. It sounds not quite right to me. But it does make sense that the EPIRB should not be inside the life raft for maximum signal. Humans and life raft material are good attenuators of RF at 400MHz.

I read once about a sad case where the captain was unaware of the water contacts. They kept the EPIRB inside the life raft thus it could not send a distress message.

This is correct as I understand it. I have read from some specification data (but I don't recall the make/model) that when floating, the radiation pattern of the antenna for 121.5 signal is omnidirectional and hemispherical for the 406 signal. I don't understand how they do that but I have no reason to doubt the claim.

[Rustic Charm]

Originally Posted by transmitterdan

Here in the US I have not seen one of modern vintage without automatic water activation. I have been told that floating the unit in water is the best way to ensure the signal is maximized. I was told the antenna is designed for maximum radiation when it is just above the water. Whether this is true or not I cannot say. It sounds not quite right to me. But it does make sense that the EPIRB should not be inside the life raft for maximum signal. Humans and life raft material are good attenuators of RF at 400MHz.

I read once about a sad case where the captain was unaware of the water contacts. They kept the EPIRB inside the life raft thus it could not send a distress message.

Well, this is interesting. I can't find any epirbs for sale in the US that are not water activated, meaning entirely manuel. This is leading me to think that it's probably legislated in the US that they can only sell water activated units. Can anyone confirm this?

My unit has 'for optimal signal strength' the unit should be placed In the water and attached via the cable to the raft.

[Wotname]

Originally Posted by socaldmax

……...
Does anyone know what older EPIRbs used, and when they started using Li based batteries? I'm sure that increased reliability just because they wouldn't be discharged when you needed them. I can't imagine batteries from 35 yrs ago lasting 5 yrs baking in a sealed device without losing a great deal of it's charge.

Alkaline batteries. They usually had a replacement period of 2 years although some (IIRC) were only 1 year. The battery packs were also physically much larger (i.e. more cells).

I have been replacing batteries in beacons since the early 80s but I not sure when the first Li batteries arrived on the scene. I can say that all the 406 beacons I have seen have had Li batteries so I assuming the two technologies arrived around the same time.

[Wotname]

Originally Posted by Rustic Charm

Well, this is interesting. I can't find any epirbs for sale in the US that are not water activated, meaning entirely manuel. This is leading me to think that it's probably legislated in the US that they can only sell water activated units. Can anyone confirm this? …....

Could well be the other way around, Aussie mandating manual only…
We do have a strange way of going against the flow sometimes, especially with respect to radio transmitters in general.

[Wotname]

Originally Posted by socaldmax

You keep arguing this point about homing in on the 121.5 MHz signal. Why bother switching to a lower power signal when you've already been flying directly toward the contact for 150 mi?

Hell, by the time they pick up a 25mw signal, they can see the whites of their eyes. At night. In dense fog.

Rather than continuing to make assertions, let's see some info from the USCG that states they switch to tracking the 121 MHz signal, right about when they're close enough to smell them.

Why are you disregarding the information contained in post 152; at least without providing some credible argument against this real life practice as used by an experienced SAR pilot with dozens and dozens of searches to his credit.

[barnakiel]

Somehow someone ASSUMED all EPIRBs are GPS enabled?

Well, not all are. In such a case 121 homing signal is the fastest way to find the beacon.

Somehow someone ASSUMED one positioning method beats two positioning methods?

Well, read some into Bowditch ...

asoasf

[Dockhead]

Originally Posted by socaldmax

You keep arguing this point about homing in on the 121.5 MHz signal. Why bother switching to a lower power signal when you've already been flying directly toward the contact for 150 mi?

Hell, by the time they pick up a 25mw signal, they can see the whites of their eyes. At night. In dense fog.

Rather than continuing to make assertions, let's see some info from the USCG that states they switch to tracking the 121 MHz signal, right about when they're close enough to smell them.

Are we still arguing about this?

Whether you like it or not, it is a fact that modern EPIRBs emit two signals: one burst signal on 406 which is intended to transmit your position to satellites, and one continuous homing signal on 121.5 mhz, which is intended for close-range RDF homing on the last mile. Is there something hard to understand about this? No one said that in some cases, with some equipment, someone might for some reason might want to do it differently -- home on the burst signal, directly decode the digital part, etc., etc,

But standard operating procedure is to fly to the coordinates given in the burst signal, then look for the 121.5 homing signal. As described on the ACR site:

"1. Distressed mariner/outdoor adventurer/pilot activates beacon (EPIRB, PLB, ELT).

"2. Beacon transmits a 406 MHz emergency message containing your Unique Identifier Number (UIN) to the LEOSAR (polar orbiting) and GEOSAR* (geostationary) satellite systems.

"3. The satellites relay the 406 MHz emergency message to a ground station called the Local User Terminal (LUT). The LUT calculates the location of the signal by measuring the Doppler shift caused by the relative movement between the satellite and the beacon and forwards the location to the Mission Control Center (MCC).

"4. The MCC continues to receive information from additional satellite passes and further refines the beacon position (2.3 nm search radius). An alert message is generated that is combined with the registration information from the database and is forwarded to the appropriate Rescue Coordination Center (RCC).

"5. The RCC makes contact with the persons listed in the database to verify the existence of an emergency and gathers additional information about the beacon users. The RCC will dispatch the closest, capable Search and Rescue (SAR) forces.

"6. Local SAR forces launch a rescue mission and use the 121.5 MHz homing signal to pinpoint the beacon."

https://www.acrartex.com/info/search-and-rescue/


Also, in the FCC examination for professional radio operators, there is a question on this very point:

7R-33E3: What may be used as a homing signal by the search and rescue vessels in the immediate vicinity of the ship in Distress?
* A 121.5 MHz emergency transmitter in a satellite EPIRB.
* Flare gun
* Strobe Light
* 406 MHz signal from a satellite EPIRB.

The correct answer is "A 121.5 MHz emergency transmitter"

The wrong answer is "406 MHz signal from a satellite EPIRB"

See: EPIRB: Homing & Locating Signals

I rest my case.


None of this is to say, and no one has said, that homing on the low power 121.5 mhz signal is always the best way to do it, or that SAR pilots ALWAYS do it like that. But that is standard procedure, and there can be no argument about it. The original statement was that homing on 121.5 signals is obsolete and not done anymore. This statement is clearly false, and surely no one continues to assert it.

[Wotname]

Originally Posted by estarzinger

…………...

Dockhead, regarding 121 homing (http://www.sarsat.noaa.gov/BMW%2008%...2008%20BMW.pdf)

"When initially developed, the electronic signal from a factory EPIRB or
ELT emanated at 75 milliwatts on the 121.5 frequency. The electronic
detection equipment installed on CG aircraft at that time was sufficient to
detect this signal.
However, the FCC subsequently mandated that the power be reduced to
25 milliwatts on the 121.5 MHz homing signal due to interference at the
higher power on aircraft emergency frequencies.
Unless in very close proximity (less than 5 NM), this lower 25 milliwatt
power falls below the threshold of effective detection with the legacy CG
aircraft DF equipment."

I can't argue with what the FCC mandated but I can argue that this is not a strong reason in a technical sense; therefore I suspect their reasons were not technical but political - and who knows what that might have been.

However I have always understood the move from 75 mW to 25 mW with the introduction of the 406 digital technology was driven more by the manufacturers than by anyone else. With the batteries available at the time, they were hard pressed to meet the 48 hour requirement and reducing the 121.5 Tx power certainly helped their designers. Note, I can't quote this as fact, rather just as informed opinion


As for the technical case:

First, a 75 mW Tx on 121.5 can't cause interference on aviation emergency channels as there is only one aviation emergency channel which is of course 121.5 MHz. The fact it is transmitting on frequency isn't interference, its doing its designated job and there are no other frequencies that it could be interfering with.

Secondly, if a 25mW Tx has so little range, then the absolute maximum range of a 75 mW Tx can only three times that - thus still very small.

Thirdly, 121.5 is almost never used in aviation emergencies in modern times (say the last 25+ years) and it certainly isn't used as a hailing channel like Marine Ch 16. Yes, it is monitored by ATC and some (many?) long haul pilots but it isn't actually used by aircraft in distress. They will be using the designated area frequency pertinent to their location and airspace.

The 121.5 transmitters (75 mW) I am referring to are those produced in the 80s and onward ever since 121.5 satellite detection/location became operational. Prior to this, the beacons produced in the 70s and perhaps earlier were quite different beasts, their transmitters were quite unstable and unfiltered, to such an extent, they were unusable for satellite detection/location. There was way too much frequency drift for satellite doppler techniques to work. They certainly produced adjacent channel interference, even with the 50KHz channel spacing in use back then.

FWIW

The photo of the cockpit panel in the link was some small twin engined Piper GA aircraft; surly not the flagship for USCG assets

[Wotname]

Originally Posted by kas_1611

Couple of things to add to the general confusion:

………..
And can someone clear up my confusion on what SSB is? Sub Sonic Biscuits? Semi Submersible Bananas? Safe Swimming Beaches? Super Supportive Brassiers? The mind boggles
……...
Keiron

I've got to think this is posted in jest as in tongue in cheek etc.

But just maybe it is a genuine question so let me say Single Side Band. Google it and all will be revealed. In the meantime, suffice to say it is a particular type of amplitude modulation utilised in marine HF radio sets.

[Dockhead]

"Originally Posted by estarzinger View Post
…………...

Dockhead, regarding 121 homing (http://www.sarsat.noaa.gov/BMW%2008%...2008%20BMW.pdf)

"When initially developed, the electronic signal from a factory EPIRB or
ELT emanated at 75 milliwatts on the 121.5 frequency. The electronic
detection equipment installed on CG aircraft at that time was sufficient to
detect this signal.
However, the FCC subsequently mandated that the power be reduced to
25 milliwatts on the 121.5 MHz homing signal due to interference at the
higher power on aircraft emergency frequencies.
Unless in very close proximity (less than 5 NM), this lower 25 milliwatt
power falls below the threshold of effective detection with the legacy CG
aircraft DF equipment.""


Sure, no argument about any of that. But "very close proximity" is exactly how the homing signal is intended to be used. SAR services get a position from the satellites to start the search, and first thing is you fly to that position. Only then do you need to do any RDF homing, and by then you'll be in "close proximity".

That doesn't mean it's infallible, or that it's the only way it's done. But that is Standard Operating Procedure, for sure.

[socaldmax]

Originally Posted by transmitterdan

Obviously if you have multiple means of communication you would use any and all of them. But the question is whether an EPIRB is no longer that useful to warrant carriage. Nothing in that story convinces me an EPIRB is useless. And an EPIRB is a dead simple device. Of all distress notification methods I think it has the least number of things that can go wrong.

I agree that EPIRBs are still very valuable rescue equipment, but I don't agree they are dead simple. I would hope they were, but the continued confusion right here in this thread about how they are deployed and activated leads me to believe that right now, a portion of the members participating in this thread, might not be able to activate their EPIRBs.

If they can confuse that many people, it needs to be even simpler, or explained better.

[socaldmax]

Originally Posted by Dockhead

"Originally Posted by estarzinger View Post
…………...

Dockhead, regarding 121 homing (http://www.sarsat.noaa.gov/BMW%2008%...2008%20BMW.pdf)

"When initially developed, the electronic signal from a factory EPIRB or
ELT emanated at 75 milliwatts on the 121.5 frequency. The electronic
detection equipment installed on CG aircraft at that time was sufficient to
detect this signal.
However, the FCC subsequently mandated that the power be reduced to
25 milliwatts on the 121.5 MHz homing signal due to interference at the
higher power on aircraft emergency frequencies.
Unless in very close proximity (less than 5 NM), this lower 25 milliwatt
power falls below the threshold of effective detection with the legacy CG
aircraft DF equipment.""


Sure, no argument about any of that. But "very close proximity" is exactly how the homing signal is intended to be used. SAR services get a position from the satellites to start the search, and first thing is you fly to that position. Only then do you need to do any RDF homing, and by then you'll be in "close proximity".

That doesn't mean it's infallible, or that it's the only way it's done. But that is Standard Operating Procedure, for sure.

I'm still waiting for some source of that info.

You know, like a cut and paste from a USCG document.

[transmitterdan]

Originally Posted by socaldmax

I agree that EPIRBs are still very valuable rescue equipment, but I don't agree they are dead simple. I would hope they were, but the continued confusion right here in this thread about how they are deployed and activated leads me to believe that right now, a portion of the members participating in this thread, might not be able to activate their EPIRBs.

If they can confuse that many people, it needs to be even simpler, or explained better.

All the EPIRBs I have seen are dead simple. Take it out of the holder and throw it in the water whilst holding on to the lanyard is all you have to do. I would submit that any other activation procedure is "not simple enough". If you have one that requires reading a book to activate don't buy one like that ever again.

[Dockhead]

Originally Posted by socaldmax

I'm still waiting for some source of that info.

You know, like a cut and paste from a USCG document.

I would have thought you could do your own Googling, but here you go:

"All 406 MHz EPIRBs have a built-in transmitting feature on 121.5 MHz that will direct SAR resources to your location when they are in the area."

Canadian Coast Guard, official site, Search and Rescue - ALERTING, DETECTION & RESPONSE - Dealing with accidents at sea - CCG - Search and Rescue


"The COSPAS-SARSAT Search & Rescue System
1) Distressed mariner/outdoor adventurer
activates EPIRB or PLB-EPIRB.
COSPAS-SARSAT Search and Rescue System 2) Beacon transmits a 406 MHz emergency message containing your Unique Identifier Number (UIN) to the LEOSTAR (polar orbiting) and GEOSTAR* (geostationary) satellite systems.
COSPAS-SARSAT Search and Rescue System
- 406 MHz Distress Signal
(2.3 nm accuracy 60 min. worldwide avg.)
- 406 MHz Distress Signal w/GPS
(0.05 nm accuracy 15 min. worldwide avg.
3) The satellite relays the 406 MHz emergency message to a ground station called the Local User Terminal (LUT). The LUT calculates the location of the signal by measuring the Doppler shift caused by the relative movement between the satellite and the beacon and forwards the location to the Mission Control Center (MCC).
4) The MCC continues to receive information from additional satellite passes and further refines the beacon position (2.3 nm search radius). An alert message is generated that is combined with the registration information from the database and is forwarded to the appropriate Rescue Coordination Center (RCC).
5) The RCC makes contact with the persons listed in the database to verify the existence of an emergency and gathers additional information about the beacon users. The RCC will dispatch the closest, capable Search and Rescue (SAR) forces.
6) Local SAR forces launch a rescue mission and use the 121.5 MHz homing signal to pinpoint the beacon.
"

EPIRB Products :: Air-Sea Safety and Survival, Inc.




"And like EPIRBs and ELTs all PLBs also have a built-in, low-power homing beacon that transmits on 121.5 MHz. This allows rescue forces to home in on a beacon once the 406 MHz satellite system has gotten them "in the ballpark" (about 2-3 miles)"

NOAA - Search and Rescue Satellite Aided Tracking - Emergency Beacons

The official website of the SARSAT system.


"Accurate Detection
Radio distress beacons operate on 406 MHz with a 121.5 MHz transmission feature being used for final stage homing.

. . .

. . .

After defining the search area, aircraft or other rescue craft rely on homing equipment to locate the beacon's exact position."

Australian Maritime Safety Authority, Australian Government official site

AMSA Search and Rescue - Australian Maritime Safety Authority (AMSA)



"2.4 The following transmitter frequency configurations are permitted in Canada:

EPIRB: 406 MHz primary transmitter and a 121.5 MHz homing transmitter.

. . .

The frequency 121.5 MHz is used as the homing frequency for EPIRBs and MSLDs."

https://www.ic.gc.ca/eic/site/smt-gs...g/sf09186.html

Canadian law on allocation of radio spectrum.


"The SOLAS convention requirements

SOLAS vessels must carry a COSPAS-SARSAT EPIRB operating on 406 MHz and 121.5 MHz. 406 MHz radio signals are used for locating purposes to detect the casualty (this is explained in details in the next chapter), while 121.5 MHz radio signals are used for homing purposes by SAR vessel/helicopter/plane involved in SAR operation which is trying to find EPIRB with the direction finding equipment."

http://www.egmdss.com/gmdss-courses/...view.php?id=59


"(b) The 406.0-406.1 EPIRB must contain as an integral part a “homing” beacon operating only on 121.500 MHz that meets all the requirements described in the RTCM Recommended Standards document described in paragraph (a) of this section. The 121.500 MHz “homing” beacon must have a continuous duty cycle that may be interrupted during the transmission of the 406.0-406.1 MHz signal only."

U.S. law -- 47 CFR 80.1061, https://www.law.cornell.edu/cfr/text/47/80.1061


A small sample. Are we really still discussing this?

[Exile]

Originally Posted by transmitterdan

All the EPIRBs I have seen are dead simple. Take it out of the holder and throw it in the water whilst holding on to the lanyard is all you have to do. I would submit that any other activation procedure is "not simple enough". If you have one that requires reading a book to activate don't buy one like that ever again.

Agreed, and the manuals are short reads & plainly written.

Unless it's a regional thing, it also looks to me that all Cat I & II EPIRBS -- at least the ones designed for boating -- are designed for automatic water activation. It's important to remember, however, that they can both also be activated manually per the switch. The water activation is a safety valve of sorts in the event your boat sinks out from under you & you cannot get to the switch in time. The Cat I's go further in that they can both automatically activate via water but also automatically deploy out of their bracket. The tether is designed to keep the units free floating with an obstructed view of the sky while staying with your liferaft or PFD.

One potential source of confusion is that PLB's, to my knowledge, do not automatically activate via water, but always have to be activated manually. Along with an ACR "GlobalFix," I also have an ACR "TerraFix" which predates my boating days but I now use as a backup on the boat. This is a PLB with a 36 vs. 48-hr. battery life and manual activation only. One drawback of PLB's is that you must keep the antenna and the body of the unit above the surface of the water for the signal to transmit properly. This could be a challenge if you have lost both your boat & liferaft as was the case with Cheeki Rafiki.