I agree.

My guess is that it didn't though, or if it did, that it didn't work as advertised.

If a GPS had been involved and working right, the position should have been reported to within 10s of meters of his actual location - assuming that he was in a spot where the unit could have gotten a GPS fix.

On one of the PLB test reports I read it seemed like a number of the units failed to provide good GPS coordinates. This info about some GPS equipped units not sending good GPS position info was also reported on some Cospas/Sarsat site documentation I read.

Do PLBs give elevation as well as L/L?

The article above said 'He had “cliffed out” on the side of Elephant Tusk...', so I am assuming that he was quite a bit above the base level. If they don't, the rangers could have been within 50' of him horizontally, but he was too high to be seen. He may have only waved the blanket when he heard/saw the chopper, but if he didn't know the rangers were below him...

Sue

Interesting . . . Checking the Cospas/Sarsat spec, it turns out that the third of a mile figure isn't all that far off from their requirements for units with a built in GPS. While it looks like the location encoding scheme accomodates greater precision than that, it only requires the following:

"4.5.5.3 Internal Navigation Device Performance

An internal navigation device shall be capable of global operation and shall conform to an applicable international standard. An internal navigation device shall incorporate selfcheck features to ensure that erroneous position data is not encoded into the beacon message. The self-check features shall prevent position data from being encoded into the beacon message unless minimum performance criteria are met. These criteria could include the proper internal functioning of the device, the presence of a sufficient number of navigation signals, sufficient quality of the signals, and sufficiently low geometric dilution of precision.

The distance between the position provided by the navigation device, at the time of the position update, and the true beacon position shall not exceed 500 m for beacons transmitting the Standard or National location protocols, or 5.25 km for beacons transmitting the User-Location protocol. The encoded position data shall be provided in the WGS 84 or GTRF geodetic reference systems.

The internal navigation device shall provide valid data within 10 minutes after its
activation. Internal navigation device cold start shall be forced at every beacon activation. Cold start refers to the absence of time dependent or position dependent data in memory, which might affect the acquisition of the GNSS position. "

Did anyone happen to see what type of PLB unit the person used?

If PLB's give elevation it would be from a GPS at best, and from what I've read that is a pretty poor measure of elevation since it is relative to the datum (I think), which (I think) can be thought of as the mathematical model of the Earth's surface (I'm weak on the whole datum idea)

I don't think its phsically possible for the doppler method (using the 406 MHz signal) can determine elevation. It just identifies the point in space - or actually a line - that is at a right angle from the source.

If there was a GPS involved my guess is that since it was on the side of a cliff the GPS didn't see enough satellites to get a good position.

Ken

While driving and passing those elevation signs in the mountains, my Garmin is easily within ~50 ft. It would probably be more accurate if I slowed down. Hiking it seems to be quite accurate relative to topo maps. But that's a 12 channel GPS receiver. How many channels does it take for a GPS to meet SARSAT/COSPAS spec? It probably has that much accuracy in elevation too. ?500 yards?

Yeah, I know what you mean.

The best explanation I've read of the PLB system is Doug's description in the PLB Test report on ETS.org. The link is http://www.equipped.org/406_beacon_test_background.htm#How - scroll down about 1/3 of the way to the How COSPAS-SARSAT System Works.

Without a GPS the PLB system uses the Doppler effect to get a position.

Picture yourself hanging out your car window while driving at a moderate speed past someone blowing a loud whistle. As you approach the whistle will sound higher pitched than it will once you've passed it. Its pretty likely that you could signal at the point when the pitch changes and fairly accurately identify the whisle's location, at least relative to the entire car ride. The LEO (Low Earth Orbit) satellites do the same thing.

If the 406 MHz beacon doesn't contain GPS location information, It can take the LEO satellites up to 90 minutes for a satellite to pass by the source of the signal, which is when the Doppler effect can be heard and a location determined. The maximum time to Doppler location decreases as you move away from the equator, so in the 48 states it will take less than an hour to get a Dopplier location. The Dopplier accuracy is about 1.5 miles.

On the other hand, GEO satellites can almost instantly receive the 406 MHz beacon with GPS location information since they are in geostationary orbits around the equator and are in constant view of large portions of the Earth (excluding the artic/antarctic areas - the LEO satellites can still see those and hear the Beacon with GPS location). The accuracy of GPS location isn't a good as a handheld GPS because some of the data is truncated (as I understand it), but it still is within about 350-600 feet.

The PLB with a preloaded GPS coordinate will provide the closest thing to a 10 second signal, but the ACR PLB will only hold that location in memory for 4 hours.

Looking at Doug's PLB test results, it looks like a PLB with a good view of the sky will take 1.5-2 minutes to be able to send the GPS location.

One thing that is interesting is that in order to save power (GPS's take relatively lots of power), once a good GPS location is obtained the ACR PLB shuts down the GPS and then it turns the GPS back on to look for a new location every 20 minutes. That seems like a reasonable comprimize to keep the 240 MHz beacon functioning as long as possible (24 hours minimum for the ACR PLB).

I'm such a geak!!

A gps that isn't used much will take a long time to get a position fix. If you use it in montana and then in texas months later it will take several minutes to get a fix. The last time I used my garmin geko 301, I thought it was broke because it was around 10 minutes to fix. After that, the other gps fixes took less than a minute on that same trip.

If I'm reading the text below correctly, per the Cospas/Sarsat spec, the beacon position can't be updated more frequently than once every 20 minutes.

The beacon shall commence transmissions upon activation even if no valid position data are available. Until valid data is available, the content of the encoded position data field of the message shall be the default values specified in Annex A. The first input of position data into the beacon message shall occur as soon as valid data is available. If the beacon has the capability to provide updated position data, subsequent transmissions of the updated position shall not occur more frequently than every 20 minutes.

If, after providing valid data, the navigation input fails or is not available, the beacon message shall retain the last valid position for 4 hours (± 5 min) after the last valid position data input. After 4 hours the encoded position shall be set to the default values specified in Annex A.

The requirement for cell phones to provide location information and volumes of units involved has had an effect on the development of newer GPS chip sets that acquire the satellites much faster - and use less power to do so. An example would be the newer GPSMAP x versions from Garmin that get fixes faster and in poorer signal environments than their previous version.

This should help newer PLBs equipped with those chipsets report initial positions quicker.

I think it has more to do with a change in location than time-since-last-use. If the GPS is far away from its last known position I think it may take a bit more time to "map" the new satellite positions. On some mapping GPS's you have an option of telling it your current location to speed things up.