a reply to: ignorant_ape
Looked into this a while back.
First, it looks like you've got things pretty well sorted out. Basically the decision comes down to a couple factors:
1. Will you ever need to communicate something OTHER than "HELP!" (i.e. send all the king's horses and all the king's men and rescue me, regardless
of cost to me or method)?
If so, you WILL need to figure on signing up for a subscription service of some kind. These start as low as about $14
/ month and go up to several hundred / month depending on what features you want. The low end of the spectrum offers only very restricted capability.
If not, then a PLB is for you, because this is all a PLB does.
On an interesting side note, PLB's (like EPIRBS, which are not hand held) are by far the best in terms of success. Basically your signal is received
by the military of whatever country you are located in and services are dispatched from there down to the local authorities. PLB's have one function,
and one only...RESCUE ME! There is no discussion.
2. What kind of coverage to you need?
Not all satellite communications are equal. Everything BUT a PLB will use commercial satellites as
opposed to military (PLB's use military / government satellites exclusively). Most of the satellite communications devices are proprietary, meaning
they communicate only with certain satellites from one company. Iridium is the best with (66) LEO satellites. Others may only be able to use as few
as 3-4 satellites. So, if a satellite isn't overhead, then your signal won't get heard. I think Globalstar is the next biggest provider with (40)
satellites. Inmarsat has (3-4).
FWIW, Garmin uses Iridium, as do many others. As you might expect, Iridium is also the most expensive. Remember, we're talking about service
providers here, not device manufacturers.
And again, because PLB's use military satellites their services are truly global. There are no monthly fees for a PLB, but again, they only send one
signal...RESCUE ME! If you do decide on a PLB, just make sure you get one with GPS. Not all of them have GPS. Because PLB communicate with not only
LEO satellites (where GPS is not an issue), but also GEO GPS on your device is important. LEO's can triangulate your location because they're moving.
GEO's canNOT triangulate your location because they are stationary with respect to the Earth's rotation, hence the need to be able to send your GPS
location to GEO satellites.
As far as subscription plans are concerned, they basically scale up as you might expect. Basic and very limited text messaging is the cheapest. If
you want voice services, plan on spending a lot more than the basic plans per month. Two-way voice AND data is the most of all (usually over $100/mo.
Lastly, a word about AIS; the primary function of AIS is for location of commercial shipping traffic. Basically like a transponder on a commercial
airliner. There isn't really any message other than "I'm here", but I guess some of them do have distress frequencies. You hit the nail on the head
though, AIS works on terrestrial VHF frequencies (not satellite), and these transceivers are located to cover locations where the heaviest shipping
traffic is, not everywhere. So, while VHF is a very long range communications band it doesn't cover everywhere. For what you are looking for, I'd
probably look for something satellite based, as opposed to terrestrial.
Hope this helps.