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[aprssig] info for TM-D710E in car

Robert Bruninga bruninga at usna.edu
Mon Jan 14 16:27:24 UTC 2008


>> This is the APRS standard for decay position reporting.
>
> I and I believe most other people would argue that 
> SmartBeaconing is the preferred way for mobiles to 
> transmit their position. The only argument
> I can see for proportional pathing in something 
> like the D710 is if it is actually standing still. 

You are comparing apples and oranges.  Decay has nothing to do
with proportional pathing nor smart beaconing.  It has to do
with ALL packets transmitted on the APRS channel.  That is, NEW
or Changing data is transmitted with a higher refreash rate
initially and then decays to lower and lower rates when the
packet is old or no longer changing.

> However, SmartBeaconing can be set for... slow beacon rate.
> For mobiles that are only parked for a short time, 10m
> For mobiles that are e.g. parked overnight... should be 
> set for a much longer period of time.

There are two specified beacon rates for APRS, 10 minutes at
events or DIRECT or ONE-HOP local use, and 30 minutes for 2 hops
or more wider area use.  So a parked car, if not turned off
altogether, should decay to 30 miunutes.  These standard rates
are there so that APRS has a consistent expectation of latency
for operating stations.

Smart beaconing has a different objective than Proportional
pathing.  Proportioanl pathing wants to make sure that locally,
a vehichle is reported more often than at a big distance.  Hence
it reduces channel QRM by an order of magnitude.  It beacons
evey minute for good latency locally, but only every other
minute do those go via a digi, and only once every 4 minutes do
they go two hops.  Thus, they are allways reporting once a
minute locally, but with reduced load further out.  Therefore
they do not need to be tweaked between a special event, or long
distance travel..  So Proportional pathing wants to keep updates
more reliable in the TIME domain while minimizing QRM.

Smartbeaconing has the objective of a more accurate track in the
spacial domain (on the map).  But all of its packets go the full
path length to all surrounding areas.

Each has merits.
Bob, WB4APR






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