Here's some information I found on the Portable Antenna for the Garmin Astro:Garmin developed this portable long range antenna especially for the Garmin Astro GPS Dog Tracking system. This accessory is designed to increase the range of the hunter's handheld receiver. When a dog travels outside the Astro's range, the antenna can be lengthened to 3 feet and attached directly to the Astro 220 via a 3 foot coaxial cable.
This new antenna is perfect for folks that need longer range for the big running bird dogs and hounds. The beauty of this antenna is that when it is closed, it gets better range than the standard antenna. When you need more range, all you do is extend the antenna out to a maximum of 3 feet and you will get better range in those heavy cover and rolling terrain situations.
The antenna features a molded handle and lanyard, and measures just a quarter meter long when stored -- small enough to be carried in a hunting vest when not in use.
