Sorry not quite correct...
The GPS constellation consists of a fleet of satellites that are all constantly orbitting and moving. Your reciever has the ability to pick up many of these and the more the merrier and the more the more accurate the fix. A minimum of three is needed for a positional fix and 4 or more will also give you altitude..
The GPS constellation as of this posting was over 32 satellites. It's likely that as many as 6 - 8 or more will be overhead with some being closer to the horizon at any given spot. Those nearer the horizon will be weaker in signal strength and your reciever will not pick them up consistently and therefor not use them.
Make sure your reciever is held steady with the antenna at top and unobstructed. GPS signals are affected by heavy tree cover, buildings, solid metal items over the antenna. Give the reciever a moment or two to lock into available signals. Also update the firmware in it to reflect the latest constellation and orbits. That is what the RX uses to run it's fixes. If that is oudated then it might be trying to track GPS satellites that are no longer in service and therefore your limiting the bird count it can use for fixes. Fresh batteries are also important as the reciever will drift if the batteries are dieing out. I recommend newer GPS units as they have better sensitiviy than the older gear.
GPS will not work in buiildings, tunnels or wherever the sky is occluded or obstructed with stuff.
Garmin, Magellan, DeLorme and numerous others make decent handhelds....
