What I'm trying to get at here is when SPOT sends a message to the satellite, does it get an acknowledgment that the message was in fact received by the satellite?
What I'm worried about is if it broadcasts without confirming an acknowledgment, you could think message went out but in fact did not.
This is no different than any 406 MHz distress beacon, or 121/246 MHz, for that matter. Distress beacons have historically been one way devices. SPOT does provide visual confirmation via the LEDs whether the transmission was sent, as with a PLB, but it is strictly a one way device.
But the core of the 406MHz PLB is a simple analog broadcast signal, right? So it just keeps broadcasting. With a data signal, if it gets missed, it's missed. No second chances. And with a data signal, a slight hiccup in signal will potentially cause the entire message to be invalid.
As I understand it, each alert is sent three times, though in the case of the OK/Check only one is passed to your contacts. I'd be surprised if there wasn't some sort of checksum done, that's SOP for all digital simplex stuff of which I am aware (406 MHz beacons included), because it is one way and there's inherently no other way to confirm it got through without being garbled, but I don't know for sure and will ask.
Yah, it sounds like maybe sending the message three times is their way of working around the issue. Not horrible, but users should understand how it works.
I assume that the 911 calls continue to broadcast over and over, but the OK check probably does not.
This would mean that it is possible for you to send an OK check/tracking and not realize it didn't get through.
-john
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