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[aprssig] help with d700 gap filler digi

Robert Bruninga bruninga at usna.edu
Sun Jan 29 15:23:55 UTC 2006


> I was playing with two d700s today side by side. 
>A small tracker was transmiting every 60 seconds. 
>Both d700s heard it, and both digi'ed WIDE1-1.
>at exactly the same moment.  This double would 
>cause me not to decode on the far end. 

Several things.
1) that is why we do not receommend mobile digis
    who all might converge to the same place
2) In your motorcycle event they would not be at
    the same place
3) Presumably you have the digis spread out to
cover the event, meaning that most of the time
they dont hear the same thing all the time
4) Presumably they are not equidistant from the
main digi

In otherwords, some pre-planning on the part of the
placement of digis can resolve this:
1) in a linear event the digis are one after another and
none at the same distance to the main digi nor to the
trackers
2) in an enclosed event, th efill-in digis are only placed
where there is a blind spot.  Also meaning no other
digis are likey to hear trackers in that area.
3) use natural shading to clearly delineate individual
digi coverages.   Or place antennas on the sides of
their poles or structures to clearly discriminate
coverage areas,etc.

You only have to have 10 dB signal differnce between
the digis when they arrive at the main digi, and there
is over 120 dB to play with, so usually there is already
a big enough difference.

But to answer your question, I guess if none of the
above are appealing then set one of them to a D wait
that is not zero.

>I'm trying to place many gap filler digis around a
>motocycle race thru the woods to copy a 5w HT tracker.

In that environment I doubt that any of the fill-in's
will both hear a tracker at the same time.  Considering
the vagaries of mobile flutter in trees.

Just some thoughts
Bob






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