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On Thu, 26 Apr 2001, Steve Dimse wrote about "The process of getting a
packet... to ariss.net goes like this:"

 [you ==> ISS==> Igate(s) ==> Internet ==> FINDU.com ==> ARISS.NET]

> The weak link here is the IGate. I've noticed that the signal from ISS 
> has strong fades in it...  The best chance of an echoed packet getting
> to an IGate is when the IGate and the  transmitting station are near
> each other, and therefore share the same geometry....

This is entirely true.  Also, though,  Steve's APRSERVE/FINDU/ARISS
system also collects duplicate packets from all other igates that also
heard the packet so there is "spatial diversity".  Only one needs to be
successful.   As long as there are a few IGates per country feeding
APRSERVE, then the probabilities quickly approach 100% of capturing every

Lets say due to fades that the chance of any Igate hearing a packet is
only 70%.  But two such stations with the same probabilities would have a
combined chance of 91% and five Igates on the East Coast would approach
99.8%.  As  Steve says, all we need are more IGates.... and ANYONE running
APRS on a PC can be an IGATE..

de WB4APR, Bob

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