The KPI for system gain is S21 and is measured in dB. It denotes the dB level difference between the output and input of the system. If the input signal is -10 dBm and the output signal is -5dBm, then the S21 is 5 dB. Even when there is a loss, it is called system gain but noted as negative. For example, if the input signal is -15 dBm and the output signal is -25 dBm, the system gain is -10 dB. Typically the gain of the programmable RFoF is 10dB and 40 dB with LNA and 15 dB without LNA. RFOptic offers units with adjustable system gain. The GUI user can turn on the LNA in the Tx unit and adjust the attenuator to get to the system gain levels needed within the link budget.