Use these SMA connectors to develop custom measurements.
The upper "B" connector comes from the coupled arm of the Port 2 coupler. The lower connector goes directly to the input of receiver "B." If Option 015 is installed, the path goes directly to a switchable attenuator and then to the receiver's input.
The upper "R2" connector comes from the transfer switch's Reference 2 output. The lower connector goes directly to the R2 receiver input.