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[aprssig] APRS vs. SPOT

Eric Hansen skyssx at gmail.com
Thu Sep 8 13:43:37 UTC 2011


They've had data tethering on Iridium forever, this is probably just a
WiFi dongle for the already extant data connection.

On Thu, Sep 8, 2011 at 9:41 AM, Earl Needham <earl.kd5xb at gmail.com> wrote:
> It isn't really Wifi, it's using a sat phone as a data connection -- I'd
> guess it's more in line with dial-up service.  Pretty slow, too.
>
> Vy 7 3
> Earl
>
> On Thu, Sep 8, 2011 at 7:18 AM, Jim Alles <kb3tbx at gmail.com> wrote:
>>
>> Iridium just announced Wifi from their satellites, good for an Igate app,
>> maybe ($$$).
>>
>> Axcess Point
>>
>> Jim A. KB3TBX
>>
>> On Wed, Sep 7, 2011 at 5:35 PM, <jjesson at voyager.net> wrote:
>>>
>>> From my ~10 years of designing-in commercial satellite/cellular tracking
>>> and telematics systems:
>>>
>>>   SPOT technology originally was designed by Axonn's then CTO and this
>>> technology is based on simplex protocol talking to Globalstar.... protocol
>>> is interesting as it chips between Globalstar's native CDMA duplex protocol
>>> (native to Globalstar). Their form of simplex is also known as send-and-pray
>>> as not an ARQ protocol with Simplex... but a form of repeat packet
>>> transmissions improve the odds of correctly receiving packets and this is a
>>> setting in their engineering configuration tool.
>>>
>>> Unfortunately, the fade margin (C/N) is marginal so trees or roof
>>> structure attenuate the signal to the point of not working and the lack of
>>> confirmation was a major issue.  Not exactly the product or wireless
>>> satellite protocol I would use if my life was riding on packet reception but
>>> ok for a lightweight tracking unit.  I used these for a quick light fleet
>>> tracking system.
>>>
>>> The new Iridium ASIC provides a true duplex portable unit and offers a
>>> solid ARQ protocol. I have evaluated their ASIC and it works great and would
>>> be my life-saving product of choice.  Hey, all the ice road truckers use
>>> Iridium tracking devices and they do bet their life on this satellite
>>> network!  One word of caution - Iridium data costs are not for the typical
>>> experimenter but if needed commercially a good deal if you need  very
>>> low-latency duplex data transmission.
>>>
>>>  Incidentally, for the best cost/packet  and if you can live with a
>>> longer latency and larger antennas - such as for heavy equipment and 53'
>>> trailer fleets - you cannot beat Orbcomm.  While both Globalstar and Iridium
>>> use L-band, Orbcomm uses 136-150 MHz for its operation.  Now you understand
>>> the antenna size issue :-)  Orbcomm is getting ready to relaunch this year
>>> and they will, IMHO, become the leader for global large asset tracking.
>>>
>>> 73, Joe Jesson, KC2VGL
>>>
>>>
>>>
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>>>
>>
>>
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