Dave wrote:
Apparently, (I do not have one) garmin has a MAGNET in the base of the
antenna (for holding it in place in a vehicle) that they ship with the
396.. (!)

The Gilsson (www.gilsson.com) external antennas work fine with Garmin
GPS receivers and sell for about $20 at:
http://stores.ebay.com/GPSgeek
These also have a magnetic mounting, but the magnets are easily
removable.