Are EPIRBs dead?

[socaldmax]

Originally Posted by Wotname

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.

Because you quoted an Aussie pilot and it can't be confirmed. You guys do everything backwards, including driving on the wrong side of the road.

Why are you ignoring the quote directly from the USCG site that says homing in on the 406 MHz signal is far more effective? That is a verifiable quote, directly from the source.

[socaldmax]

Originally Posted by Dockhead

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.

This is from the USCG NAVCEN site, not Canadian or Australian.
Emergency Position Indicating Radiobeacon (EPIRB)

406 MHz EPIRBs

The 406 MHz EPIRB was designed to operate with satellites. The signal frequency (406 MHz) has been designated internationally for use only for distress. Other communications and interference, such as on 121.5 MHz, is not allowed on this frequency. Its 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). These devices are detectable not only by COSPAS-SARSAT satellites which are polar orbiting, but also by geostationary GOES weather satellites. EPIRBs detected by the GEOSTAR system, consisting of GOES and other geostationary satellites, send rescue authorities an instant alert, but without location information unless the EPIRB is equipped with an integral GPS receiver. EPIRBs detected by COSPAS-SARSAT (e.g. TIROS N) satellites provide rescue authorities location of distress, but location and sometimes alerting may be delayed as much as an hour or two. Although these EPIRBs also include a low power 121.5 MHz homing signal, homing on the more powerful 406 MHz frequency has proven to be a significant aid to search and rescue aircraft. These are the only EPIRB types which can be sold in the United States.

A new type of 406 MHz EPIRB, having an integral GPS navigation receiver, became available in 1998. This EPIRB will send accurate location as well as identification information to rescue authorities immediately upon activation through both geostationary (GEOSAR) and polar orbiting satellites. These types of EPIRBs are the best you can buy.

406 MHz emergency locating transmitters (ELTs) for aircraft are also available. 406 MHz personnel locating beacons (PLBs) are available.

The Coast Guard recommends you purchase a 406 MHz EPIRB, preferably one with an integral GPS navigation receiver. A Cat I EPIRB should be purchased if it can be installed properly. An EPIRB can also be rented from multiple providers. It can save your life.

Since this USCG source mentions interfering signals on 121.5 MHz, then also states that homing on the more powerful signal is a significant aid to SAR aircraft, it leads one to believe they home on the 406 MHz signal. It makes no mention of homing on the 121.5 MHz signal in the last mile or so.

Why use a homing signal that is also used by other resources, possibly leading the SAR unit astray? If multiple contacts are transmitting on the exact same frequency, it's very difficult if not impossible to discern which is which, especially if you're listening to the signal to help guide you.

As a matter of fact, that's why they reduced the signal strength of the 121.5 MHz signal from 75 mw to 25 mw, to reduce possible confusion and interference with airborne homing beacons.

Your FCC test question is probably outdated, after all, who knows better what procedures the USCG actually performs, the USCG, or the FCC? My money is on the USCG.

[Dockhead]

Originally Posted by socaldmax

This is from the USCG NAVCEN site, not Canadian or Australian.
Emergency Position Indicating Radiobeacon (EPIRB)



Since this USCG source mentions interfering signals on 121.5 MHz, then also states that homing on the more powerful signal is a significant aid to SAR aircraft, it leads one to believe they home on the 406 MHz signal. It makes no mention of homing on the 121.5 MHz signal in the last mile or so.

Why use a homing signal that is also used by other resources, possibly leading the SAR unit astray? If multiple contacts are transmitting on the exact same frequency, it's very difficult if not impossible to discern which is which, especially if you're listening to the signal to help guide you.

As a matter of fact, that's why they reduced the signal strength of the 121.5 MHz signal from 75 mw to 25 mw, to reduce possible confusion and interference with airborne homing beacons.

Your FCC test question is probably outdated, after all, who knows better what procedures the USCG actually performs, the USCG, or the FCC? My money is on the USCG.

You can do your own reading and draw your own conclusions.

That source talks about homing on 406 as A significant aid. A possible supplement to the normal procedure of homing on 121.5. It does not say that homing on 121.5 is not done, or that it's not the normal procedure.

The FCC test is current, and "Homing on 406" is still the wrong answer


Here a USCG source which describes the procedure:


"406s also send out a weaker signal on 121.5 MHz. This is because most rescue craft use direction finders that tune to that frequency. The 406 signal will locate you to within a few miles, at which point rescue craft will home in on the 121.5 MHz signal to pinpoint you. If you take nothing else with you offshore, this device is a must."

USCG: D11 Off Shore Search and Rescue

and another:

"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)"

http://www.uscg.mil/hq/cg5/cg534/Eme...sofbeacons.doc


"Front Cover: A 406MHz EPIRB brought the Coast Guard HH-65 close
enough to spot the partially sunken F/V STILL CRAZY XII; the crew had
drifted away, but the 121.5 MHz homing signal led rescuers to their location.
Read more starting on page 16. Photo provided by Gregory
Johnson, MSO Charleston."

http://www.uscg.mil/hq/cg5/cg534/On%...e/OSFALL03.pdf

[Dockhead]

Originally Posted by socaldmax

Why are you ignoring the quote directly from the USCG site that says homing in on the 406 MHz signal is far more effective? That is a verifiable quote, directly from the source.

It might very well be more effective, for some purposes, like homing from 150 miles away, as in that example.

But nowhere does it say that this is normal procedure -- because it's not.

[transmitterdan]

Originally Posted by socaldmax

Why use a homing signal that is also used by other resources, possibly leading the SAR unit astray? If multiple contacts are transmitting on the exact same frequency, it's very difficult if not impossible to discern which is which, especially if you're listening to the signal to help guide you.

As a matter of fact, that's why they reduced the signal strength of the 121.5 MHz signal from 75 mw to 25 mw, to reduce possible confusion and interference with airborne homing beacons.

Actually the reduction to 75mW didn't help the SAR crews much. It helped a little bit with the 48 hour battery life requirement. The SAR crew would like to get as big a signal as possible.

The reason 121.5MHz is useful for direction finding is that it is transmitted continuously. It is much easier to DF with your ears using a continuously transmitted tone than the 406MHz which is a very intermittent signal. There is no way the EPIRB can continuously transmit on 406MHz as that would break the overall satellite system.

The people that write stuff on web sites are human. They make mistakes. I suspect what they meant was that the newer GPS enabled EPIRBs can be decoded in the aircraft without the delay of the satellite data going all over the world before it reaches the crew. They are not direction finding from the 406MHz signal, they are decoding it in the cockpit and using the coordinates to guide them to the beacon. A web writer might be forgiven for not being into all the details. But when the aircraft gets close the 121.5MHz signal gives the pilot a real time course to the target. And the crew does not need to translate GPS coordinates into a heading. They just have to listen to the tone to select the best heading.

Really this debate is kind of silly. All EPIRBs have a 121.5MHz homing beacon and USCG use it as do most other SAR teams around the world. It is not going away.

[socaldmax]

Originally Posted by transmitterdan

Actually the reduction to 75mW didn't help the SAR crews much. It helped a little bit with the 48 hour battery life requirement. The SAR crew would like to get as big a signal as possible.

The reason 121.5MHz is useful for direction finding is that it is transmitted continuously. It is much easier to DF with your ears using a continuously transmitted tone than the 406MHz which is a very intermittent signal. There is no way the EPIRB can continuously transmit on 406MHz as that would break the overall satellite system.

The people that write stuff on web sites are human. They make mistakes. I suspect what they meant was that the newer GPS enabled EPIRBs can be decoded in the aircraft without the delay of the satellite data going all over the world before it reaches the crew. They are not direction finding from the 406MHz signal, they are decoding it in the cockpit and using the coordinates to guide them to the beacon. A web writer might be forgiven for not being into all the details. But when the aircraft gets close the 121.5MHz signal gives the pilot a real time course to the target. And the crew does not need to translate GPS coordinates into a heading. They just have to listen to the tone to select the best heading.

Really this debate is kind of silly. All EPIRBs have a 121.5MHz homing beacon and USCG use it as do most other SAR teams around the world. It is not going away.

I disagree with this statement. The FAA has been campaigning for some time to shift from 121 to 406 for aircraft beacons. The main resistance has been airplane owners who don't want to spend $1500 for a 406 beacon when they can still get a 121 beacon for $500.

I predict at some point in the future, (possibly distant future) there won't be anyone using 121 for SAR homing, it could possibly revert to voice comms for air to air use or something else.

Think about it, if COSPAS/SARSAT/everything else SAT assets no longer receive 121 beacons, and 406 beacons are all they receive and they are 200 times stronger, why wouldn't aircraft take advantage of that emergency beacon infrastructure already in place?

Pride? Stubbornness? Cheapness? Don't care? None of those are valid excuses.

As for DFing a 250ms signal burst, it's easy. A good DF receiver can take multiple DF cuts and average out a number of cuts (say 8-10 for good measure) and give you 2 averaged DF readings in less than 250ms. That's true DFing - when the equipment calculates a bearing to the contact based on signal phase measurements. Flying a plane and changing directions while listening for changes in volume to a warbling tone is archaic and highly inaccurate, especially compared to good DF system bearing accuracy.

That's like having a laser guidance system on your car, but preferring to swerve left and right and bouncing the tires off of the Botts dots. Sure you can do it that way, but why?

[socaldmax]

Originally Posted by Dockhead

It might very well be more effective, for some purposes, like homing from 150 miles away, as in that example.

But nowhere does it say that this is normal procedure -- because it's not.

So you're saying that they posted their abnormal procedure on their website, but made no mention of their normal procedure.


Okaaaaaaaay...

[transmitterdan]

Originally Posted by socaldmax

So you're saying that they posted their abnormal procedure on their website, but made no mention of their normal procedure.


Okaaaaaaaay...

Actually what they said was not at odds with what Dockhead is telling you. You seem to be equating the term "direction finding" and "homing". They are not the same thing. It is entirely possible that homing on the 406MHz signal is nothing more than decoding the coordinates and then setting a course for those coordinates. That is not what 121.5MHz direction finding does.

[socaldmax]

Originally Posted by Dockhead

You can do your own reading and draw your own conclusions.

That source talks about homing on 406 as A significant aid. A possible supplement to the normal procedure of homing on 121.5. It does not say that homing on 121.5 is not done, or that it's not the normal procedure.

The FCC test is current, and "Homing on 406" is still the wrong answer


Here a USCG source which describes the procedure:


"406s also send out a weaker signal on 121.5 MHz. This is because most rescue craft use direction finders that tune to that frequency. The 406 signal will locate you to within a few miles, at which point rescue craft will home in on the 121.5 MHz signal to pinpoint you. If you take nothing else with you offshore, this device is a must."

USCG: D11 Off Shore Search and Rescue

and another:

"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)"

http://www.uscg.mil/hq/cg5/cg534/Eme...sofbeacons.doc


"Front Cover: A 406MHz EPIRB brought the Coast Guard HH-65 close
enough to spot the partially sunken F/V STILL CRAZY XII; the crew had
drifted away, but the 121.5 MHz homing signal led rescuers to their location.
Read more starting on page 16. Photo provided by Gregory
Johnson, MSO Charleston."

http://www.uscg.mil/hq/cg5/cg534/On%...e/OSFALL03.pdf

OK, there we go, exactly what I was asking for and couldn't find myself.

Thanks, I believe it now.

[transmitterdan]

Originally Posted by socaldmax

That's like having a laser guidance system on your car, but preferring to swerve left and right and bouncing the tires off of the Botts dots. Sure you can do it that way, but why?

That is not even a close analogy to the situation. 121.5MHz is not used by satellites. It is used by the search team to precisely locate the beacon once they get to the vicinity of the 406MHz transmitted coordinates.

Maybe it will help to explain the technical details. 406 MHz beacons transmit at fairly high power (5 watts) for 250mS immediately when turned on, and then transmit a digital burst once every 50 seconds thereafter. That works well for notification of a problem and it greatly saves on battery power. But it is woefully inadequate for a DF system to only get an update about once per minute. DF systems (and human ears) work best with a continuous tone. That's why 121.5MHz should still be in any 406MHz beacon even on aircraft. The 121.5MHz signal can lead a human searcher with a simple DF set right to the beacon. No need to wait for an incredibly short signal once a minute.

[Wotname]

Originally Posted by socaldmax

......

As for DFing a 250ms signal burst, it's easy. A good DF receiver can take multiple DF cuts and average out a number of cuts (say 8-10 for good measure) and give you 2 averaged DF readings in less than 250ms. That's true DFing - when the equipment calculates a bearing to the contact based on signal phase measurements. Flying a plane and changing directions while listening for changes in volume to a warbling tone is archaic and highly inaccurate.......

OK, I do note that you are finally convinved about the way the system works and praise the lord for the good old USCGwebsites.

However for completeness, the issue with 406 homing is not the ability of the equipment to provide a bearing to the the transmitter because you have explained yourself, DFing a 5 W UHF is always going to better than 25 mW VHF signal. The issue for the pilot is the delay in getting updates of the bearing.

He will travel somewhere between 1.5 miles to 3 miles (or more) depending on the machine he is flying between fixes. When the search area is say 5 miles, these updates are way to slow, he will be overshooting while waiting for new updare. Of course the 121.5 Tx is continuous so the bearing to the target is always real time data.

And for Aussie SAR pilots, well it is true they are used to having the car steering wheel on the right side of the car and just like USCG helo pilots they fly their heli from the right side so I reckon they are alright and can be trusted.

If you are ever in our search region and you have to pop the EPIRB, they will come and get just like those trusted USCG guys.

In fact, if you are ever downunder and around 43 S, I will hunt you down, buy you a beer and introduce you to some of them. Heck, they might even buy you a beer, unless of course they have rescued you, in that case they will be expecting you to buy.

And for other readers who may be geographically challenged, there isn't much of Australia around 43S so we are easy to find.

[Wotname]

Long live 121.5
Regardless of all the chatter in this thread regarding low power 121.5 transmitters being limited to 25 mW, there are EPIRBs with 50 & 75 mW transmitters.

GME, Ocean Signal and Kannard all list some models with 50mW 121.5 transmitters while Salcom list one with a 75 mW transmitter.

These are currently available and approved in Australia and NZ. I can't comment on their availability in other countries.

FWIW, I have also found some GME units that are restricted to AU/NZ only and other manufacturers making units for AU/NZ only.

[socaldmax]

Originally Posted by transmitterdan

That is not even a close analogy to the situation. 121.5MHz is not used by satellites. It is used by the search team to precisely locate the beacon once they get to the vicinity of the 406MHz transmitted coordinates.

Maybe it will help to explain the technical details. 406 MHz beacons transmit at fairly high power (5 watts) for 250mS immediately when turned on, and then transmit a digital burst once every 50 seconds thereafter. That works well for notification of a problem and it greatly saves on battery power. But it is woefully inadequate for a DF system to only get an update about once per minute. DF systems (and human ears) work best with a continuous tone. That's why 121.5MHz should still be in any 406MHz beacon even on aircraft. The 121.5MHz signal can lead a human searcher with a simple DF set right to the beacon. No need to wait for an incredibly short signal once a minute.

I understand how it works. You missed the most important part of that post.

How RDF units can give you multiple DF readings in less than 250ms. It simply doesn't require a continuous tone. Thus my analogy. Once the RDF unit gives you a bearing, you're pointing right at it, no need to constantly update.

It's always best to use the strongest signal (especially 5w vs 25 or 50 mw.) It's always more accurate to use the higher frequency signal. It's more accurate to take multiple DF cuts, then average those results for a displayed bearing. Those aren't my opinions, those are established facts of DF system design.

As for DFing a 250ms signal burst, it's easy. A good DF receiver can take multiple DF cuts and average out a number of cuts (say 8-10 for good measure) and give you 2 averaged DF readings in less than 250ms. That's true DFing - when the equipment calculates a bearing to the contact based on signal phase measurements. Flying a plane and changing directions while listening for changes in volume to a warbling tone is archaic and highly inaccurate, especially compared to good DF system bearing accuracy.

Using human ears to listen to a warble is like wandering all over the lane hitting the Botts dots, compared to the vastly better bearing accuracy of an RDF unit giving bearings to a higher frequency transmitter. It's not like the life raft is doing 50 kts, it's pretty much just bobbing around, or moving with the current, so bearing shift isn't going to be much compared to aircraft closing rate. By the time they're within a mile or two, they're going to be yanking and banking, looking for the survivors visually.

[Wotname]

Here is a FCC aproved EPIRB with a 50 mW 121.5 Tx.
Kannard Safelink Sportpro.

It certainly looks like the FCC has changed it's stance on the 25 mW restriction.