Actively Curious wrote:I read you post somewhere else about the SPOT not being a "real" PLB, OtherHand.
Sure....PLBs must meet Federal certifications as to minimum transmit power, battery life and durability. There are all sorts of standards they have to meet. With a SPOT it's whatever the manufacturer feels like doing. As an aside I have opened up my SPOT once and I was a little appalled at the workmanship and quality of the circuit board.
When you press the Help button on a SPOT it goes to a private company, I think in Texas, that then decides what authority to contact, if any. With a PLB the emergency signal goes to an Air Force Rescue facility in Virginia. They then begin to activate standard rescue channels. It's their job and they know what to do.
The satellites listening for PLBs are SARsats, dedicated search and rescue satellites operated by the US and other governments. SPOT uses the Globalstar satellites which are privately run for the purposes of sat phones and the like. And until recently, the Globalstar constellation sucked donkey balls as compared to the Iridium satellites, but SPOT can't use those (the DeLorme InReach does though). Globalstar has got better with more satellite launches, but for a variety of reasons it's not extremely reliable.
A SPOT has a transmit power of 400 milliwatts. A PLB has a transmit power of 5 watts. That's 12.5 times more transmit power. But there's even more to it than that. SPOTs use a frequency of 1.6 GHz, while PLBs use 406 MHz, a much lower frequency. This lower frequency penetrates things (like forest canopy) MUCH better than 1.6 GHz. This lower frequency has about 4 times the penetrating power of the SPOT frequency. Combine this with the much larger transmit power and you have a device much more likely to hit a satellite in marginal conditions than a SPOT.
PLBs have multiple ways to signal for help. In the event they can't get a GPS fix, they still emit the 406 MHZ signal that the SARsats can locate to within a few kilometers with doppler techniques (takes a couple of orbits though). PLBs also emit a signal on 121.5 MHz which is an international aircraft frequency (as in ELTs) and can be tracked by rescuers. If a SPOT can't get a good GPS fix....well, you're out of luck.
Finally, the PLBs with their SARsat coverage of the globe is essentially 100%. The things will work anywhere on the planet, except maybe at the bottom of a deep mineshaft. SPOTs are limited to the coverage are of the Globalstar satellite constellation, which is only parts of the globe.
Don't get me wrong, I'm not bashing SPOTs (well, I guess I am). I have one myself, but I no longer use it. SPOTs are great for what they are, a way of letting people who want to follow what you are doing know where you are in a non mission-critical way.
The way I usually put it is like this: If you press the button on a SPOT you will probably get help. If you press the button on a PLB you WILL get help.