First lets look at the high bandwidth RF Signal Generator. Performance priorities include providing a phase stable and phase coherent LO, with the ability to maintain phase coherency over extended periods of time. Additional priorities include flexible programming of frequency, power and phase on each channel, with clean adjustments and switching, long term phase memory and overall low phase noise. 

The Berkeley Nucleonics Model 855B offers excellent Phase Coherence because of several design features.

• Each channel has a common, highly stable OCXO frequency reference
• Frequencies of all channels are digitally synthesized
• Frequencies of all channels are derived from the common reference with high resolution
• Homogeneous frequency synthesis circuitry for parallel channels (ensures maximum phase coherence, inter-channel frequency stability)
• Channels all share the same ambient conditions (eliminates drift, etc)
• Each module features a pair of high frequency clock ports (synchronization between Model 855B units)