Epirb testing, what happens, and, battery life - techy..

captainslarty

captainslarty

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Hi all
Just pondering, when you test an epirb, is a signal transmitted to a sat and then received back ?.. it would appear so ??

Also, re battery life.. I would be interested to know IF a test is ok, can the emergency use of the unit be gauranteed to last the quote 24 or 48 hours ??..

Hmmm, ponder ponder...
 
No, your EPIRB does not Tx and Rx from the satellite; it only transmits on 406MHz and the reception is done by a large ground station antenna at around 1.6 GHz.

My understanding is that when you perform a self test the beacon does not transmit (or at least at such a low level that it is below the receive threshold level of the satellite receiver). Don't know if a successful test is any indication of battery life expectancy.

Alan.
 
I believe that the EPIRB does Tx to the satelite and get a signal back. I can't remember where I got this info from.

The bateries in an EPIRB have a very long shelf life, and are guaranteed to transmit for 48 (or 24) hours at the coldest temperature, at the end of the five year period. This is the time that the manufacturers say that the batteries should be changed. They will transmit after this date, but not for the guaranteed duration. The older the batteries the shorter the Tx time. If you use them in warmer conditions they will last a bit longer.
 
From the US coastguard website:

Testing EPIRBs
406 MHz EPIRBs can be tested through its self-test function, which is an integral part of the device. 406 MHz EPIRBs can also be tested inside a container designed to prevent its reception by the satellite. Testing a 406 MHz EPIRB by allowing it to radiate outside such a container is illegal.

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. These EPIRBs also include a 121.5 MHz homing signal, allowing aircraft and rescue craft to quickly find the vessel in distress. These are the only type of EPIRB which must be certified by Coast Guard approved independent laboratories before they can be sold in the United States.

Not trying to be a "smart-ass" but this is an important concept.

Alan.
 
Just to reiterate an EPIRB does not have a receiver as part of the beacon unless it has a GPS receiver which provides location data constantly which can be encoded onto the beacon signal.

Battery condition is confirmed by a successful test but this is not a good indication of expected life. However the use by date (replace battery date) is the best indication of time to replace battery.

When buying an EPIRB look at cost and availability of replacement batteries. It can make all the difference to cost of ownership.

In aviation there was one brand of beacon 121.5 that used 8 Duracell D cells. These were replaced each year but the cost was so cheap compared to the specialised batteries of some beacons. And of course the capacity and performance was very good.

good luck olewill
 
My EPIRB has a magnet in the bracket that disconnects the battery using a N/C reed relay so no power drain when in mounting bracket for long battery life
 
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