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[aprssig] Group tracking

John Goerzen jgoerzen at complete.org
Tue May 1 00:18:37 UTC 2012


Hi Bob,

That would be easily done on the TH-D72a.  (Do you mean that a single 
packet goes out with WIDE2-1,WIDE2-2 , or were you giving me settings 
for different transmissions in the proportional ring?)

The VX-8GR does not support proportional pathing.  I am thinking that I 
should set it to either WIDE1-1 or WIDE2-1 and just leave it like that.  
It seems it would be likely to provide good enough coverage most of the 
time (I think it would be rare where one station has a good copy on one 
digi, and the other on a different).

Thanks for the tips.

-- John

On 04/30/2012 05:47 PM, Bob Bruninga wrote:
>
> 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 1/4^th 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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