Add another dog to your current SportDOG Brand electronic collar system or replace a lost or broken collar receiver with the SDR-FS Add-A-Dog Receiver. The original collar receiver for the FieldTrainer SD-400, this unit can be used with any SportDOG Brand FieldTrainer , SportHunter SD-800, WetlandHunter SD-400CAMO, ProHunter, UplandHunter SD-1850, or HoundHunter SD-3200 transmitter.