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[aprssig] Mobile Digi (TEMPn-N)

Stephen H. Smith wa8lmf2 at aol.com
Mon Jun 15 17:13:18 UTC 2009

William McKeehan wrote:
> Why would it be a bad idea for the D700's to run around with WIDE1-1 enabled
> all of the time?

1)   You wind up with an unstable, constantly-changing network as 
mobiles move around:

o     Either the fixed digipeaters cover an area adequately, in which 
case extra mobile digis are irrelevant and just add channel congestion .  
o     The fixed infrastructure does have coverage holes, but  users can 
never count on fill-in coverage at given locations since mobiles are 
constantly moving around.     

2)   You get massive numbers of unnecessary additional digipeats most of 
the time, resulting in a massive increase in channel loading.  Imagine 
the QRM mess and amount of air time consumed  if 5 or 10 mobiles a few 
miles apart in the afternoon rush hour all try to digipeat each other's 
packets constantly.   Then consider the hundreds of duplicate packets 
hitting the local WIDEs from all those mobile digipeats added to the 
home fill-in digipeats.  

3)   For everyday use, mobiles make terrible digis since they:

o     Are lower to the ground than even home WIDE1-1 fill-in digis, and 
lack useful antenna height.
o     Are usually moving.   The data bit-error rate (which causes RX and 
TX failures) due to mobile flutter goes up rapidly as the speed increases.

BOTTOM LINE:  Unless a mobile is PARKED and STATIONARY on high ground 
(hill top, top of a parking ramp, etc), they are adding to the problem 
(by creating channel congestion, and possibly adding to the number of 
defective packets) rather than helping. 



Stephen H. Smith    wa8lmf (at) aol.com
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