Re: birding-aus GPS, EOW, Y2K, etc.

Subject: Re: birding-aus GPS, EOW, Y2K, etc.
From: Paul Taylor <>
Date: Tue, 31 Aug 1999 13:48:11 +1000
"Lawrence E. Conole" wrote:
> Recently the EOW (end of weeks) event rolled over, and I haven't seen
> any reporting of outcomes here.  I guess that reflects the modernity of
> most birders' GPS units?!?
As promised, my Garmin GPS II+ didn't miss a beat.  I had hoped to watch
the EOW rollover by downloading the before and after almanac data, but
I miscalculated the changeover time based upon US timezones instead of
GMT/UTC and missed it!  Oh well, there's still Y2K. 

> Mine is an antique by most standards - a Garwin GPS38 running version
> 3.04 software.  It had trouble on the EOW day (22/8/99), and despite
> leaving it on in a big clearing for ages, it couldn't sort itself out.

It's academic now, but did you try Page+On? (i.e. hold down the Page
button, turn the unit on, then release the Page button.)  I believe
that this clears just the almanac data, so that the unit will go
immediately into the almanac acquire mode and skips trying to use
its out-of-date almanac.  Using Page+On, you need to leave the unit
somewhere with a clear view of the sky for 15 to 30 minutes to
complete the almanac download process.

N.B. this sequence only works for some Garmin models (including the
GPS 38 and II+).  You should *not* experiment with these types of
keystrokes unless you know what you are doing; for example, on these
models Mark+On clears *everything* in the memory: waypoints, tracks,
almanac data, temperature calibrations - the lot.  This will take a
*long* time to recover from, and should only be used in an "if all
else fails" situation.

> I downloaded the software fix from the Garmin WWW site and uploaded it
> into my GPS.  Since then it seems to have upped its performance
> somewhat.

This seems to be a common report on the sci.geo.satellite-nav 
> The EOW problem was clearly resolved by the software fix, but I'm
> curious about why the overall performance has improved - maybe the
> software upgrade did more than fix the day/date problem??  On my recent
> trip, the venerable old GPS38 was doing hot fixes in about 1-2 seconds -
> that's faster than ever before.  Some hot fixes were almost
> instantaneous.

The GPS 38 doesn't have a firmware upload facility (the firmware is
stored in a write-once EPROM that must be returned to Garmin to be
updated), so you are running the same firmware you had before the
EOW rollover.

>From the documentation, the EOW fix program appears to just upload
a new time value to the unit to help speed up acquisitions during
the first week or two of the rollover.  This should take only a
second to upload; if it took 15 seconds or more, I would suspect
that they transferred the week 0 almanac data as well.  

I would guess (as others have speculated) that your performance
improvement is as a result of getting a complete almanac data download
from the satellites or the EOW fix program; having up-to-date satellite
data greatly improves the start-up time of any GPS unit.

An interesting idea: you should be able to "jump start" a Garmin GPS
if you have a second Garmin GPS with a current position fix and a
Garmin-to-Garmin data cable (or a Garmin-to-PC cable and appropriate
software to act as an intermediary.)  Since the unit with the position
fix will have the current time and almanac data from the satellites
(or at least enough of it to get a position fix), sending this data
to the other unit should allow it to warm start without having to
download the data itself from the satellites.  The same procedure
should work with other brands of GPS (or even different brands),
provided you have the appropriate data cable and the units have a
common data transfer protocol (or the computer software can convert
the data into the necessary format.)

   Paul Taylor                           Veni, vidi, tici -
                    I came, I saw, I ticked.
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