The 70900B is the master control module for the modular spectrum analyzers and surveillance receivers. It is also a component of the lightwave signal analyzers. The 70900B LO has two main functions in the Keysight 70000 spectrum analyzers: as the synthesized local oscillator (LO) and as the master control module for the system. As a spectrum analyzer local oscillator, it affects phase noise, stability, and frequency accuracy. The 70900B is the reason that the analyzer has excellent phase noise performance of -108 dBc/Hz at 10 kHz offset from the carrier. The synthesis technique has millihertz resolution for accurate frequency control. The fast tuning speed of the LO directly relates to the tuning speed of the analyzer. As the master control module, the Keysight 70900B determines system features, slave module control, command processing speed, and GPIB speed. The combination of hardware and processing power provides fast tuning for surveillance applications and automatic testing.