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[aprssig] Group tracking

Bob Bruninga bruninga at usna.edu
Mon Apr 30 22:47:29 UTC 2012


Simple answer!

 

Proportional pathing for the caravan with WIDE2-1,WIDE2-2 path.  Everyone
hears everyone else at a one minute rate for up-to-date live situational
awareness but most of your packets are direct and do not bother anyone in
the area.  Half of your packets may make it to a local digi, but only 1/4th
will bother the surrounding area.  Same goes for hiking.

 

Bob, WB4APR

 

From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of John Goerzen
Sent: Monday, April 30, 2012 5:41 PM
To: TAPR APRS Mailing List
Subject: [aprssig] Group tracking

 

Hi folks,

I'd like to get some recommendations on beacon configuration for group
tracking scenarios.   The main scenarios I have in mind are:

1.	A caravan of 2 or 3 vehicles traveling to a common destination.  The
trip could be 30 minutes or 15 hours, could involve a mix of highway speeds
(75 MPH) and city speeds (20 MPH or less).  The point of APRS tracking would
be to give at least one vehicle the means to find the other if needed, due
to getting separated in traffic, taking different exits, loss of cellphone
communication, etc.  The vehicles will usually, but conceivably not always,
be within simplex range of each other (owing to lack of external antennas
and high speeds in some cases).
2.	Hikers in 2 groups in a large park/wilderness area.  A similar goal
as before - give at least one group the means to find the other assuming
nothing but APRS beacons as communication.  Here I would assume that the
hikers will be within simplex range (say, a mile or two) of each other at
5W.

One could also add other similar scenarios, such as coordinating search and
rescue parties, tracking SKYWARN volunteers, etc.

There are a few special things about these scenarios:

1.	We may not usually care about getting frequent position updates.
During the minutes / hours in which one party is not trying to locate the
other, we don't care too much about getting frequent updates.
2.	When one group is trying to locate the other, default position
update timings will likely be way too long.  For instance, 5 minutes or even
2 minutes at 70MPH is a lot of miles and a lot of potential exits that may
or may not have been taken.  A lot of SmartBeaconing scenarios have 30
minutes between beacons at 20MPH, which is unreasonable for tracking someone
in city traffic.  (And, according to my reading, could actually be even
longer at speeds between the low and high speed, oddly enough)

One could conceivably use a TinyTrak AIO or similar device for the group
being tracked, though in my particular case it will likely be a locked
VX-8GR.  Neither the TinyTrak nor the 8GR responds to APRS position query
packets (?APRSP), so that is out.  The TH-D72A does, but it is also larger
and for various reasons is also the stronger tracker device.

For the hiking scenario, we could conceivably use a 440 frequency since it
is unlikely that a digipeater would be of any help at all.  This puts less
of an importance on restricting transmit rates.  A lot of testing suggests
that battery drain on APRS HTs is usually due to engaging the RX side, not
the TX side, so I would not have battery concerns on a simple 1-minute
interval.

For the car travel, we would probably want to use WIDE1-1 (are there any
digis that would answer to WIDE2-1 but not WIDE1-1?) to get a little help
from nearby digis, due to the likelihood of greater separation and more
challenges to RF signals getting out.  It seems a bit annoying to have a
1-minute beacon going from a restaurant parking lot for an hour on 144.390,
but perhaps it is not as bad as I am making it out to be.  It seems that if
I set the low speed on SmartBeaconing to, say, 5MPH to prevent this, and set
the high rate to 2 minutes and the low rate to 5 minutes, it would lead to
some very long intervals at, say 10MPH (70/10*2 is 14 minutes).  An odd
little gap in the SmartBeaconing design, that.

What are suggestions to both meet the objectives and be friendly to other RF
users?

Thanks,

John
KR0L

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