SportDog SDR-AH Add A Dog Collar for Training Collar SD-3225The SDR AH Add a Dog Receiver Collar expands your SportDog training system, allowing you to train multiple dogs with a single transmitter. Specifically designed for use with the HoundHunter SD 3225 and compatible with a range of SportDog models, it arrives with a blue strap for quick dog identification and reliable field performance. Expandability: Add a Dog Receiver Collar expands your SportDog setup to train additional dogs using one transmitter.