[pct-l] smartphone as GPS

[Gary Wright]

On Oct 25, 2010, at 6:55 PM, dsaufley wrote:
> Dunno, and couldn't quote the guy precisely, but that's the gist of what he
> said.  No doubt there's an engineer/technical person out there that can make
> better sense of it.  Techno-peasant that I am, I'm simply beguiled with the
> thing, and am surprised every day at what it can do.   If one of the
> whiz-kids out there can show me how to get GPS capabilities on the PCT
> without a tower signal, I'd be interested in learning.

Most smart phones give you a variety of ways to control how many 'radio'
functions are active at any time. And most of them have got quite a few
'radios' and/or radio modes:

  -- voice service
  -- 2G data service
  -- 3G data service
  -- Bluetooth
  -- WiFi
  -- GPS

The general rule is that the more 'radios' you've got on, the higher the
drain on your battery.  If you want one of these devices to last in the
backcountry you should turn off as many of those functions as possible
and only enable them when needed.  Airplane mode is usually a good way
to turn off everything and still let you use the device for non-radio
things (games, camera, apps, etc).

Most apps that use the GPS will give you some way to control how often
the GPS receiver is active.  Make sure you check this out and understand
how to ensure the GPS receiver is turned off when you aren't using the
application to avoid running down the battery while you phone is sitting
in your pocket.

Running apps in the "background" will also drain your battery and so you
should understand how to avoid this and it differs from one vendor to
the next (Android/iPhone/Blackberry, etc).

I'm pretty confident that if your device is in a 'hard-off' position, as
opposed sleep/standby mode, that your battery is pretty
safe from being drained.  Of course if you want to take your phone out
and snap a picture or look at a map you'll have to wait for it to start
up, which will always be longer than if it was just in 'sleep' mode.

I got a ride from Independence up to Onion Valley in 2004 with a guy who
programmed GPS units and asked him why they battery life for these
devices was so terrible.  He said that the satellite signal is quite
weak and that the amplifier in GPS units sucks up the power.  I found
this with some google searches:

> The GPS signal strength measured at the surface of the Earth is
> about –160dBw (1 x 10–16 watts), which is roughly equivalent to
> viewing a 25-watt light bulb from a distance of 10,000 miles


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