SPOT Satellite Messenger Debuts at Outdoor Retailer

SPOT Inc., a subsidiary of Globalstar, introduced its subscription-based SPOT Satellite Messenger which is being promoted as a multi-purpose tool that can used as a distress beacon as well as providing options to request help without a full blown Search and Rescue response. It can also be used to notify friends, family or associates that you are okay and as a means to track your location. Join us as we take a preliminary First Look to see if we're willing to consider betting our life on SPOT at this juncture.

http://www.equipped.org/SPOT_ORSummer2007.htm

Thanks for the great comments about this product.

I agree 100% that a distress call should be put through regardless of if the unit can get a GPS fix or not. This seems a very poor decision on their part.

I also disagree with the idea of not putting through 911 messages w/o a subscription. The reality of it is IMO that this will change later anyway after they have their first mishap. Death or injury, lawsuits, and then a change of policy. Best to find a business model that works in this regard up front.

I do have a couple of specific questions. Since the unit is considered a "one-way" communications device, I am curious if the actual underlying data protocol is one way as well.

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.

Further, is there some sort of checksum incorporated into the data protocol to ensure the message was not garbled in transmission? If so, what happens if it was? Does it re-send, give the user an error, etc?

Thanks for your report Doug!

-john

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.



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.

End-to-end ....
does this means :
- a location is transmited and a signal is sent back to the unit to acknoledge the location translmission
or
- a location is transmited and you have to access some web site to check if the signal correctly arrived at the other end
??????
The first explanation would mean two-way communication, but you say there is none ;
The second explanation would mean you have no way to test in the field, only at home/office ;
So, what is the third, correct, explanation I have been to dumb to understand ??

Or does "end-to-end" applies to the unit only (from pushbutton to antenna), not the entire system, satellite and Geos response center included ????


TIA

End-to-end refers to the entire system. You have to be able to either check the web site or be able to check with one of the contacts that would receive a text message (which could also be yourself). The whole point of conducting a self-test is to do it before you go, not once you are in the field. Self-test is to ensure everything is working at a point in time that you can either repair or replace before it is critical. It provides confidence that the device will work when you need it to. Once you are already in the field it's too late, there's nothing to be done about it at that point.

All in all, it sounds better to me than OnStar, which a lot of folks think is a cureall for traveling problems/emergencies. At least this one you can carry around with you...

Oh .. thanks .. now, I get it ...

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.



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

That is incorrect. The 406 MHz transmission is digital. That's how they can include all the identification data. Old 121.5/245 MHz beacons are analog. The 121.5 MHz homing transmission in PLBs is analog. 406MHz is Digital.



That isn't necessarily a correct assumption. They may well do a checksum. We don't know.



The 911 transmits until the battery is dead.



Life is uncertain. Eat dessert first.

You can only do so much with the tools available. That issue is inherent in any simplex system. That's why good designs take measures to increase the chances the message gets through. A good example of that is their triple transmission. They may well have other mitigation strategies, I don't know.

On-Star is great, for what it is. It is not a panacea. It's a lot better than nothing, usually works better than your handheld cell in marginal areas of cell coverage and I know folks who were very glad they had it. As you note, many, if not most users expect more than it can deliver in some situations. Most don't realize it is cell based. On-Star is NOT a satellite based system, it is cellular .