I am looking for a small, lightweight, self contained GPS datalogger
that can record positions for several months.  The unit should be less
than 50 grams, and be able to run on a predetermined duty cycle until
retrieval, at which point data can be downloaded.

A good answer will have links to such a product, or a combination of
products that allow logging of GPS points while still being under 50
grams.  The unit or combination of units should also be suitable for
outdoor use.

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Clarification of Question by jtmandel-ga on 12 Jun 2003 19:17 PDT

I am happy to tip if this price is too low for the question.

I expect that the device simply does not exist.  Given your weight
limit, I would assume the device is to be worn by an animal (maybe
human?).  This would imply there is not a power source available.  To
give an idea, 50 grams is the weight of two AA batteries
(http://www.duracell.com/oem/Pdf/MX1500.pdf).  I don't know the power
requirements for GPS receivers, but this may be a limiting factor.

Something I just came across in EE Times is the Wherify GPS/PCS
wristwatch marketed to parents.  The article, which shows innards of
one of these, can be found at
http://www.eetimes.com/story/OEG20030519S0072 and the company that
makes the device can be found at http://www.wherifywireless.com/. 
This device does not log and can give only 40 "locates" in 60 hours. 
I expect this is mostly due to the device having to keep in contact
with PCS cell towers.  This does give you an idea of what is going to
go into the device you seek and suggests that it's possible.

Certainly the beginnings of an interesting project. :)

Good luck,
Bradley

There is a GPS watch made by Wherify that weighs close to 50 grams.
It's designed to be worn by kids to monitor where they are so it's
made to be as light as possible.
I saw it at http://www.gpsexplorer.com/gpslowa.html while shopping for
a marine GPS unit for my boat. I hope this helps!