One of the recurring issues is wether to include a navigation system on-board, or to rely entirely on the (very able) capabilities of the rescue team's goniometers. The main issue with our experiments is the limited weight of the payload, and the resulting restrictions for power consumption.
Until now - I have not found low-cost GPS boards that are also low-power. Generally, they either consume over 150 mA and do not have any serious sleep or power-down mode (see other GPS)
An intermediate solution seems to be the Vaisala 'GPS' - the quoates because it is not really a GPS, just the 'satellite finder' part of the GPS. Check this page dedicated to the results obtained.
An entirely different solution is the use of the VOR signals from several airports. I've found some references to this type of navigation, but no real results. This promises to be be the lowest-power solution of all.
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