For radio signals that are higher that 1 GHz (1000 MHz) in frequency, they visit the B-rack which down-converts the signal to within the frequency range of 500 - 1000 MHz.

The signal is down-converted to the range of 500 - 1000 MHz because the equipment that processes the signal in the Data Acquisition system can only operate between 500 - 1000 MHz.

(Signals that are lower than 1 GHz go directly to the Data Acquisition system via the cables.)