[Xastir] More system questions

[Tom Russo]

On Thu, Jun 28, 2007 at 03:20:11PM -0500, we recorded a bogon-computron collision of the <RiverRidge at CenturyTel.net> flavor, containing:
>  For a portable digipeater .....
> 
>  *) Steel ammo-can.  >  $20 at Sportsmans Guide

We use waterproof high-impact plastic containers, not ammo cans.

>  *) Large gell-cell.  >  $190 for 55AH Optima Deep Cycle Marine
>  *) Mobile antenna mounted to the lid, perhaps a 1/2 wave antenna so
>    that it doesn't require a ground plane.  >  $45 

We have several options, including a tripod-mounted mast, roll-up wire
antennas, etc., chosen to fit the need.

>  *) 2-meter handheld radio.  >  $130

I'd probably go with a cheap mobile rig instead of a handheld.  Doesn't need
to be fancy, just something you can tune to 144.39 and wire up to the KPC-3+.
Could be a used unit you get at a swapfest.  By using something barebones
you might find a perfectly servicable unit getting offloaded for cheap because
it isn't sexy enough for today's standards.

>  *) Kantronics KPC-3+ TNC, set up to digipeat.  >  $180

Specifically, you would probably want it set to digipeat as a callsign
substitution (MYALIAS) digi, with an alias of WIDE1-1 --- only because this
is a nice generic fill-in digi alias, and folks wouldn't need specially 
programmed trackers to participate in on your missions.  Once you have gotten
set up to work with APRS well, you're going to want to start bringing your
other agencies/teams into the fold, and having a standard set-up is A Good 
Thing.

>  *) Perhaps a chain to lock it to a tree in case a stray hiker finds
>    it during the mission.  >  Free!! (my garage supply house) 
>
>  System about $515

Might want to add in whatever is neccessary to guarantee that the gell cell
is always fully charged.

>  Since the battery is 55 AH and the Kantronics list a 30ma draw that equals a 
>  long time , Right?

Not exactly right.  The kantronics might only draw 30ma, but the radio will 
probably draw an amp or two while it transmits, and probably more than 30ma 
while receiving.  It *should* be a low duty cycle, though, so it shouldn't be 
drawing that much that often.  If you're using a handheld, you don't want to 
rely on its NiCd or NiMH battery, you want it powered off of the gell cell, 
too.

>  Given this.....  what does this do for you?   Where would you want it in 
>  relationship to the radios in the field? 

A digipeater's purpose is to retransmit data from other stations.  If you
had good mountaintop digipeater infrastructure in your search area such that
you could reliably get a digipeater to hear your teams, you don't need the 
portable digi.  The assumption is that you either *don't* have a nearby 
mountaintop digi, or that there are significant gaps in its coverage right 
where you're most likely to be operating.

The portable digi's purpose is to fill-in gaps in digipeater coverage so 
your field team's data can make it to the place where the data is needed.
So you place it where it has a good view of the places where your teams will
be working, and either a good view of the command post/base camp/whatever,
or is in a good place where another digipeater can hear it well.

Either way, your goal is to make sure that data from field teams get heard by
the base station with the display --- either directly from the trackers,
via a single hop through your portable digi, via a mountaintop digi, or
via a chain including both your portable and mountaintop digi.  Running 
trackers in the field that can't be heard by your base station display 
is pointless.

The alternative that Curt's advocating (which I say again has yet to be
proven, and is hard to do with readily available equipment) is to create
an ad-hoc network of man-portable digipeaters on the theory that each 
field team should be within simplex range of some other field team,
and that the whole collection of teams ultimately contains at least one
who is in an area that can either be heard directly by base or by a
high, wide (mountaintop?) digi.  In both approaches you're trying to set
up a network that boosts the range of an individual tracker so that it 
can get heard by the folks who need the information being produced.

-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM
"And, isn't sanity really just a one-trick pony anyway? I mean all you get is
 one trick, rational thinking, but when you're good and crazy, oooh, oooh,
 oooh, the sky is the limit!"  --- The Tick