Abstract: A portable GPS receiver unit is attachable to the underside of a portable computer and has a GPS antenna mounted for sliding movement into and out of a receiver housing. During periods of non-use, the antenna can be stowed within the receiver housing to provide a highly compact and portable unit. For usage, the antenna can be protruded from the housing to obtain a clear view of the sky. The antenna is made easily removable from its movable support surface so as to enable the antenna to be remotely placed. This can be accomplished by a magnet attached to the antenna which is attracted to the support surface, and which can be used to secure the antenna to other surfaces having a clear view of the sky, such as an automobile roof.