Agilent / HP The 66321D Mobile Communications DC Source provides fast transient response, exceptional sourcing, output resistance programming, and precision measurement. This product is specially designed for testing next generation digital wireless communications products. The 66321D mobile communications DC source offers a new capability that simulates the internal resistance of a battery or battery pack. Additionally, these high performance models offer improved transient response and stable output operation with either short or long load leads. The unit provides 0 to 15 V and 0 to 3 A.