GPS Stuff

Current info: Eagle Explorer/Expedition II - 12 channel parallel channel model

The Expedition II is essentially an Explorer with more waypoint capacity and an audible alarm - the electronics & software look pretty similar.

Good points:

NZ Grid Reference is displayed
Uses 4 AA size cells (alkaline,lithium) - rechargeable accessory available.
Sealed & waterproof.
Reasonably lightweight.

Weight = 260 g (without batteries)
Weight = 310 g (with 4 x lithium AA - 50 g)
Weight = 345 g (with 4 x alkaline AA - 85 g)

NZ Grid Reference format is displayed as :

2647325 E
6464053 N

On the Waitakere 1:50 000 Topomap (260-Q11 & Pt. R11) the Grid Ref would normally be quoted as 473640 (happens to be Mt Donald McLean) and this equates to the 100 metre accuracy.

Once proficiency is gained I guess a real hero could use the Spanish grid or something just for a challenge - joke!

List of NZ Grid References.

Note: Quality shows the quality of the fix - the smaller the number of metres the better and the more satellites visible (& lockable) the better.  Since May 2000 Selective Availability has been disabled ( Presidential decision - SA enabled reduced the accuracy of GPS fixes to within 100 metres 95% of the time) so 20 metre accuracy should be possible most of the time.

3 satellites are required for an accurate 2D position fix.

Experience tends to suggest that prior to using the GPS in a particular area it should be turned on for a while (c. 20 mins or so) in order to fully locate the satellites. After this most fixes should be acquired within a minute or so. I have also found a cheap cover for the unit for added protection - a Nokia cellphone case from the markets.

Personal Note: Some people may be worried that GPS units will be useless if the satellites fall out of the sky - this is true however should the 24 odd satellites suddenly commit harikiri I probably won't be in a position to worry about it, I'll be looking for the tin hat! The usefulness of the GPS is increased hugely if you remember to also carry the relevant topographical maps (NZMS 260 series for NZ) so the Grid Ref's can be plotted.

Note 1: The location of this fix was just above the footbridge at the Lewis Pass exit in a small clearing surrounded by quite thick trees. This reading took a long time to lock in ( c. 10 mins) because the 3 satellites were all high in the sky. A fourth satellite towards the horizon managed to appear and this improved the fix time so it appears that if the required number of satellites are bunched then it may have trouble getting a fix.