Agilent 66321D 

The Agilent 66321D 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 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 66321D dc source provides all of the capabilities of the 66321B with the addition of a built-in digital voltmeter