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Old 01-25-2008, 12:25 PM   #180
Gnarly Adventurer
Joined: Nov 2007
Oddometer: 140
Originally Posted by aciurczak
I don't think the GPS portion of the antenna is the hard part. At this point in the technology curve, gps receivers are almost microscopic, and the necessary antennas are tiny and quite effective. Including the one on the SPOT, which picks up a GPS signal easily while inside the garage.

It's the transmission back to the satellite network that is the engineering problem. With a GPS antenna plugged into a garmin, it's easy for a user to see if the signal strength went up, are there less drop-outs, etc; right from the display. With the SPOT's communication back to the satellite, it is sent blind with no confirmation available (until you check online to see if one awhile back got through). And getting that antenna right evidently has much less room for error. And are there even available external satphone antennas for such devices (perhaps there are, but I haven't searched yet). As in spotmakers post, how would one know if the add-on antenna was helping, hurting, or indifferent; other than just noting that the transmitter wasn't working as well as they expected.

Personally I'd like the additional functionality if it could be put into a v2 or v3 unit, but I wouldn't categorize its removal as being patronizing to customers; getting that antenna exactly right for a reasonably high success rate transmitting back to the satellites is evidently a key engineering point for the gadget.
The decision of "no external antenna" was primarily made by SPoT Inc. (Globalstar) as they were 100% in charge of specifying the user interface, feature set, appearance, etc. We at Axonn were primarily in charge implementing what they wanted.

However, we did not protest the decision of no external antenna all that loudly.

You are absolutely correct. Making an external antenna work on the GPS is not all that hard. Getting the transmitter to work with an external antenna involves a lot more complexity, and not all of that complexity is technical. A lot of it is regulatory.

Every transmitter and every antenna that transmits on the Globalstar network has to be approved and certified by Globlastar as well as by the FCC.

Do you know how many antennas Globalstar has certified for their simplex network? Two. And it was a looonnggggggg process to get those certified!

The radiation pattern and power are held to an extremely tight envelope.

I've heard stuff like "why don't you just jack up the power a bit?"

The power output on the SPoT is riding right at Globalstar's maximum allowable.

Let users fiddle with antenna gains, radiation patterns, or power and all kinds of hell is going to break loose, Globalstar is going to be pissed, and the FCC is going to issue fines. This is a licensed transmitter (license held by SPoT Inc). It's not just a receiver.

Since the SPoT uses a combination transmit/receive antenna, allowing the connection of just an external antenna for GPS would open a technical can of worms.

Those of you who would like to design a transmit antenna, are you willing to go through the Globalstar and FCC certification process?
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