[aprssig] Backpack Portable Battery Specs

Robert Bruninga bruninga at usna.edu
Tue Feb 26 08:58:42 CST 2008

> ... I've operated ... APRS from the White Mountains 
> using just AA's [using] the D7 and a GPS receiver.  
> > I'm thinking about "backpack portable" with
> > a full-blown TNC/transceiver(average) 2 amp-hours

A tangential response:

The GPS and VHF Receiver are the biggest power hogs by a huge
factor.  The transmitter for APRS is usually insignificant..
And for APRStracking, at a hiking pace, you usually don't need
either the GPS or Receiver most of the time.

So rather than lug a battery that is 10 times larger than needed
just to power the receiver and GPS which are not needed most of
the time, you might consider leaving them off except for when
you need a fix.

In fact, leave the GPS at home too and carry a 1 oz map.  Most
hiking maps have lat/long coordinates, and most hikers know
where they are.  So, just key in your lat/long into your D7  at
each rest stop, TX a few times, and then turn everything off.
In fact, you don't even need a map.  Before the trip, just jot
down an approximate LAT/LONG for key landmarks say, every few
hours along the trail.  Then with this tiny list, you can
interpolate where you are and enter in pretty good estimates of
position all day long.

If you really want continuous tracking, consider what we are
doing for our Buoys, that is, turning on the GPS for 30 seconds
only every N minutes.  Then turning on the TNC for the last 5
seconds of that time.  Then waiting 5 more seconds and turning
on the Radio just in time to TX the posit and then shutting
everything down until the next cycle.

GPS takes typically 50 mA?
RX takes typically  50 mA?
TX takes 500 mA for 1% of time averaging 5 mA

So you see, the GPS and receiver are the biggest power hogs by a
factor of 10 in battery consumption.


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