406 mhz EPIRB

406MH epirbs will only transmit their exact position if you buy the GPS option and have it connected to a gps.

without GPS they will still be more accurate than 121.5.

BTW, ACR Electronics make a Personal Locator Beacon (PLB) which is probably what you would be wanting. Check out www.acrelectronics.com/terrafix/ for details of their "land" version or search their site for the aquafix version. They (aquafix) retail about $700 at whitworths etc (non GPS version).

Andrew

Yes Kim, it's unfortunate that many people have no idea how to prepare for the unlikely event of an emergency.

It's like saying "the chances of my house burning down are a million to one - why should I waste money on insurance against such an unlikely event"

EVERY aircraft has the ability to detect and home in on a 121.5 EPIRB - that won't change.

>The use of 121.5 MHz epirbs may even become
>illegal not long after that date

They can't prosecute me until after they have rescued me :)

As Mike point out; 121.5 and 243MHz will always remain emergency frequencies and aircraft will alert S&R of an EPIRB - personally I'll stick with my VHF unit until UHF prices come down to a sensible level.

I have my doubts the the VHF sats will all be switched off in 2008 anyway.

Mike Harding

Can someone explain to me how a geostationary satellite makes "passes" in order to locate your beacon. Aren't geostationary satellites suppose to be continuously over the same spot on earth? Or have I got that wrong?

R.

TV and communications satellites are geostationary and 36,000km out in space.

Others are not geostationary.
GPS satellites orbit every 12 hours at 18,000km.
Globalstar Satphone sats are at 1400km
Iridium Satphone sats are at 700km

Robak,

Unless i'm mistaken, there was no mention of geostationary sats "passing" over any areas.

Quite simply, there is currently 2 systems at the moment, with the older LEOSAR being replaced by the geostationary GEOSAR system. Australia is covered by 2, and in some areas, the possibility of 3 GEOSAR sats.

Check out Site Link for all the info...

I would guess 121.5 and 243Mhz would still be used as a homing frequency for some emergency services for some period of time afterwards if the signal is available via the epirb.

Andrew

LEOSAR will ALWAYS be needed, as GEOSAR cannot determine the position of an EPIRB that does not have a GPS input.

yep, sorry....my mistake :-(

::pushes edit button on EO site::

::changes the words "replaced by" with "supplements"::

Andrew

Andrew,

I just got a little confused as Kiwi Kia said:
"An alert signal from an 406 MHz recieved by a geostationary satellite will immediatly be passed to a rescue co-ordination centre."
and
"the exact position of the beacon is fixed as it takes two passes from an orbiting satellite to fix the position of a non-gps type beacon."

But I guess he was referring to the new and the old system. Is that right?

So with the new system do you need to have a GPS attached since it is a geostationary satellite?

Oh it's all to confusing....

Cheers

R.

LEOSARs can locate 121.5 to 20kms and 406 EPIRBs to 5kms after a few passes.

GEOSARs can immediately locate a GPS equipped 406 EPIRB to hundreds of metres. They can immediately identify a non-GPS 406. They do not receive 121.5 EPIRBs which put out 1/25th the power of a 406.

All aircraft and helicopters are able to receive 121.5 EPIRB signals and SHOULD have their second COM radio set to this frequency, but it's not too likely on smaller aircraft.

To locate a signal will require multple passes by the aircraft at lower altitude

All 406 EPIRBs have a 121.5 transmitter to allow aircraft to home in on it.

hey robak,

Check out the table at the bottom of the page with the link i provided earlier:

Site Link

Helps greatly with your questions.

Andrew

Thanks andrew.

I also read kiwi's response below. It's all starting to make sense.

Cheers

R.

and who would have thought a kiwi could make sense ;-)

Andrew

Mike wrote:
___________________________________________
"EVERY aircraft has the ability to detect and home in on a 121.5 EPIRB - that won't change" and:

"All aircraft and helicopters are able to receive 121.5 EPIRB signals and SHOULD have their second COM radio set to this frequency, but it's not too likely on smaller aircraft.

To locate a signal will require multple passes by the aircraft at lower altitude

All 406 EPIRBs have a 121.5 transmitter to allow aircraft to home in on it."
____________________________________________

Sort of correct, Mike. While all aircraft with a VHF transciever can receive (and report) the triggering of a beacon, the ability to home on the beacon is limited to aircraft fitted with direction-finding equipment (ie. search meter). At the moment, that is limited to specially equipped SAR aircraft, and certain military aircraft.

All airline aircraft routinely monitor 121.5 on COM2, whenever not using it for other operational matters. Some pilots (to the chagrin of the rest of us) even use 121.5 for chat....Grrrr.

EVERY aircraft which can receive 121.5 can localise the transmitter - DF equipment just makes it very easy.

Standard procedures are published based on using acquisition and loss of signal and then tuning slightly off frequency to reduce receiver sensitivity when close in to the transmitter.

Yes Mike, I'm aware of homing procedures. However it is neither taught during pilot training nor requested of aircraft (by SAR authorities) in flight (well never in my 25+ years as a pilot). The last time homing procedures (no azimuth guidance ala DME homing) were taught as a syllabus item, was back in the early 80's, and even then it was an add-on for an instument rating that very few people ever took up.

The point I'm trying to make is I would not want to depend on having a non-searchmeter equipped aircraft being asked to participate in a homing-based search. The overwhelming majority of pilots would not know (and don't need to know) how to conduct one.

A typical response to a triggering nowadays is for ATC to seek info, such as when did it start/squelch enabled/disabled/loudest signal/signal fade. Once this info is gathered I imagine AUSSAR uses the data to plot the various data on a map to get a search area.

Mike DID - The old methods of "boxing" a signal went out with whistle-stop tuning! :-)) Man that's a looong time ago.

This system is also rather useless in mountain or deeply incised topography.

I am not sure that modern PLL radios are easily tuned 'slightly off frequency'.

Someone mentioned 243 MHz - this is military stuff ONLY

FACT:
New COSPAS satellites DO NOT have a 121.5 MHz reciever.

FACT:
The old COSPA satellites have reached the end of their use by date.

121.5 MHz WILL be phased out sooner rather then later, it will not be kept operating with bandaids.

As John R said; "The last time homing procedures (no azimuth guidance ala DME homing) were taught as a syllabus item, was back in the early 80's"

When RPT crews detect a signal on 121.5 they report the acquisition and loss location which will be used by the RCC to localise the source.

Any type of receiver will have reduced sensitivity on an adjacent channel that can be used for close-in localising.

Every transmission on 121.5 will be rigorously tracked down even when it is suspected to be not a critical situation . One reason for this is that a beacon triggered in the marina could mask or confuse a beacon triggered in anger up to 12 miles away . The other reason is that a beacon in an unlikely position could still indicate a real emergency . After JAN09 sattelites wont listen for 121.5 , and the number of aircraft routinely listening on 121.5 wont be large , but you could still use the old beacons by nominating them on your remote area travel information . When you dont arrive an aircraft would search on 121.5 .

>The 406 mhz will activate a satellite immediately and not
>wait until a satellite passes overhead.

Given that radio transmission at these frequencies is "line of sight" only I would be interested to know how a UHF EPIRB can communicate with a sat. until it "sees" it?

Mike Harding

The satellites are in geosynchronous orbit that means they are essentilly stationary and rotate with the earth.

A read of this site will answer all the question that have been asked.

There is a section on bushwalkers using EPIRB's and the al the answers should be found here.

Site Link

>A read of this site will answer all the question that have been asked.

So you don't know then?

Mike Harding

A geosynchronous satellite with a very high gain antenna might be able to pick up a low-powered EPIRB, but how would it locate the position of the EPIRB ???

The COSPAS SARSAT satellites are in low earth orbit at an altitude of 528 miles - have a look at www.sarsat.noaa.gov/satellites1.html.

As they move over the surface of the earth they transmit the shift in frequency of the received signal to the groundstation so it can determine where the EPIRB is.

There are TWO satellite systems involved in the picking up and tracking of EPIRB's.
The COSPAS - SARSAT system consists of a mixture of LEOSTAR (Low Earth Orbit) and geostationary satellites. There are at present six American and two Soviet satellites.

The geostationary satellites are positioned so that their footprints monitor most of the earths surface except at high lattitudes as you approach the poles. The low earth orbit satellites are in polar orbits and unless your epirb is fitted with a gps then it is these that are used to fix the beacon position.

The 'new' 406 MHz epirbs also put out a signal on the 'old' frequency of 121.5 MHz and this is used by aircraft to home in on when at close range to the beacon.

The position of an epirb is located by TWO successive passes of a low earth orbiting satellite and it could be from 2 1/2 hours up to nearly 7 hours till your psoition is fixed. The satellites use the doppler effect to locate the position of an epirb by listening to the signal get stronger as the satellite gets closer. However, the satellite can not determine if the beacon is 'left' or 'right' of its track across the surface of the earth so two possible positions are recorded. On a second pass two more possible locations are noted, one of these will be the same as the first pass and this will be the location of the beacon.

The geostationary stellites IMMEDIATELY pass an epirb signal to a rescue centre. The low orbit satellites can ONLY pass on a signal if they can "see" an earth recieving station at the same time as they "see" an epirb.

With 406 MHz system, in some cases, it will be rather obvious where a signal is comming from if one of the two possible positions is on land and the other position is at sea. As soon as contact has been made with an owner nominated person and the rescue centre has been told that the beacon is on a 4wd on land then a sea contact could be discounted.

The important thing about the basic 406 MHz system is that a distress signal is recieved and rescue processes are started immediately. Exact location of the beacon will still take a couple of hours.

I would also assume that because in most cases 2 GEOSAR satellites will be picking up the signal and sending it on to the LUT for processing (great, either NZ or India in most cases ;-)), they should be able to eliminate the incorrect location due to triangulation. I can just see it now.......those kiwis answering the call from a Indian call centre :-)

Andrew

That sounds logical Andrew but it does not happen that way unfortunately.

The only sure way of getting your location immediately transmitted to a rescue centre is to use a registered, gps equipped epirb. I am of course assuming that the epirb has been placed in a position where it can 'see' a large portion of sky eg. not down in a narrow canyon or in a steep sided mountain valley.

"The important thing about the basic 406 MHz system is that a distress signal is recieved and rescue processes are started immediately"..... Kiwi Kia I hate to burst your idealistic bubble about EPIRBs but that's not quite telling the whole story. After spending 2 weeks out in the desert with a Seargent in the search & rescue sqaud I can add that although the duty officer may start making enquires as soon as the unit is activated, depending on the time of day, the area the signal is coming from & the availability of aircraft etc etc, he suggested to me that if they don't have a 2nd sourse to corroborate, often it's nearly 24 hours before a search may actually begin & as much as a further 24 hours before ground crews are sent in.
There appears to be a false expectation by many that if one was to set off a 406 that rescue will normally be at hand within 2 hours when after my discussions with a member who coordinates these search's that is rarely the case.
Cheers Craig............

Hi Crackles,

"...and rescue processes are started immediately.." I can assure you that they are 'Started' immediately. The situation is assesed, contact with nominated parties is attempted, information about the possible location, numbers in party, pre-existing medical conditions, age of party members, current and forecast weather conditions, checks on availability of assets (aircraft, ground, sea, manpower) in the area, etc. etc. In some cases assets may be put on standby and are ready to 'go' as soon as hard data on a specific location comes to hand.

In my previous posts I have indicated that it can be up to seven hours (worst case) before low orbit satellites can confirm an exact position of the activated beacon.

A 121.5 MHz beacon needs to have a satellite not just 'in range' of the beacon but the satellite must also be able to 'see' a ground recieveing station at the same time. This set of circumstances may not occur on each pass of the satellite and so a ground station may not even be alerted for several hours. It could then take many more hours to get an exact ground location of the beacon.

Unfortunately for 121.5 "exact position" from the satellite, means within 20km and for 406 within 5km.

If you're under good tree cover, it will be hard even for an aircraft to find the actual incident, unless they can home in on the beacon.

I spent many days on ground searches looking for VH-MDX at Barrington Tops (there was no beacon signal in this case) and it still hasn't been found !

I wouldn't buy a 300Mhz version........no-one would pick up the signal ;-) I take it you mean an epirb using the VHF range (121.5 Mhz). The last thing we need is another frequency thrown into the equation ;-)

Andrew