The Agilent 8657D signal generator adds Pi/4 DQPSK digital modulation capability to conventional AM, FM, and pulse modulation formats. The Agilent 8657D builds on the excellent performance of the Agilent 8657 signal generator by adding digital modulation capability. The Agilent 8657D provides the performance to test mobiles for North American Digital Cellular (NADC) and Japanese Digital Cellular (PDC) radio systems.