Another thing with the eTrex series. The aerial is the 1 inch square silvery thing you can see just under the plastic above the screen. You need to hold the unit flat in your hand with the screen facing up for best reception. If you've got it on a lanyard hanging round your neck you'll find you won't get such a good signal.
Also, take a look at the satellite display screen. It's not uncommon on some days to have no satellites directly overhead but several on the 45 degree line. If you view to the horizon is obscured by hills or trees that again can reduce the signal quite substantially. Have a look
here for a screen shot of what I'm referring to.
Chris
Graculus
Volunteer UK Reviewer for geocaching.com
UK Geocaching Information & Resources website
www.follow-the-arrow.co.uk
Geocaching.com Knowledge Books