Personal Locator Beacons…

[steven franchuk]

I normally carry my Plb in my pack, but should I have it in my pockets or around my neck?

When I hiking it is strapped to my hip belt or sholder strap. When I am not hiking it attached to the seatbelt in my car. In both cases I can easily get to it with one hand.

[Garth Collier]

I carry mine in a cuben shoulder strap pocket supplied by Zimmerbuilt…i fitted this to my GG Gorilla…..the McMurdo PLB fits in very nicely.

[Bob Gross]

"Bob: so the Cospas-Sarsat satellites are geo-sync?"

Cospas-Sarsat actually has two types of birds. The primary type is geosynchronous. That means 22,000 miles up over the Equator. The secondary type is low earth orbit, and they are non-geosynchronous. I think the primary type is for the primary mission over the normal latitudes, and the secondary type aids for the polar latitudes and for some other duties.

"What about polar coverage? Aren't geo-sync satellites over the equator? So at may lat of 60.5N, they would be a maximum of 29.5 degrees above my horizon? And, within one area, it would always be at a fixed bearing and height?"

Don't be silly. Why would anybody want to live north of 60N? Just joking.

Yes, geosynchronous satellites are over the Equator, and in some cases they have a little trouble reaching the polar latitudes with signals. Yes, they will appear to be low in the sky. One particular satellite will appear to be in a constant position in the sky. However, there are multiple satellites with some overlap in coverage.

"Something could be 25,000 miles out, but in a polar orbit, but then wouldn't be geo-sync and a constellation of them (3 or 4?) would be needed to continuously cover both poles."

25,000 miles out is not a common orbit. Nor do geosynchronous "birds" fly polar orbits. I can't exactly imagine how you could park a satellite over a pole. The most common birds flying low polar orbits are military spy satellites. GPS birds are flying inclined polar orbits, so that is sort of a compromise between geosynchronous and polar, so GPS birds are coming up over one horizon and then disappearing over another horizon.

I talked to some U.S. Army Signal Corps antenna experts, and they were involved with GPS reception back in the very early years before GPS was even known to exist publically. They had been on the ice north of Barrow, and they were trying to receive the first two or three GPS satellite signals. It was very bad then, but this was back around the 1980's. The assumption is that there is very little going on at the polar latitudes, and therefore there is little point in trying to optimize these various satellite systems to provide superior service there.

I also talked to the guy who was the engineering design project leader for GPS back then. Gee, did that guy have GPS stories to tell.

–B.G.–

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