GARMIN 010-11049-00 Astro DC 30 Wirelesss Collar Transmitter Transmitter Collar For The Astro(R) Dog Tracking System GPS Receiver & Vhf Transmitter On Collar Weighted Collar Keeps Transmitter Unit Under DogS Neck While Flexible GPS Antenna Stays Pointed Toward The Sky For Optimal Performance Dog Position Updates Every 5, 10 Or 30 Sec 7-Mile Range, Depending On Terrain