Keysight 81160A - 7.15 Coupling between Channels

Tutorial
81150A and 81160A User’s Guide 651
7.15 Coupling between Channels
Introduction
Each of the two channels of the Keysight 81150A / 81160A uses its own
DDS as time base for the signal being generated. This allows using the two
channels completely independently, just as if they are two independent 1
channel instruments that use the same reference clock.
In some applications, the 2 channels are not used completely independently,
but rather require some synchronization between the two channels.
Frequency Coupling
When enabling frequency coupling, the output frequency of channel 2 is
derived from the output frequency of channel 1 (except for frequency
sweeps).
The frequency of channel 2 is defined as follows:
12
Frequency
Divider
Multiplier
Frequency 
Whenever the frequency of channel 1 is changed, the frequency of channel
2 is adjusted automatically according to the above formula. All other
settings of channel 2 are still independent of the settings on channel 1.