Aviation - Air to Ground VHF Communication

Optic fibre is sometimes used in satellite communications to convey RF analogue signals (up to several GHz) between a central building and remote antennas, possibly several miles away. This means that the radio modems (with associated data cables, tuning and modulation controls) are located in the base building and all that is needed at the antenna is the receive LNA/LNB plus transmit BUC. I don't know if airports use such fibres to connect their VHF radios to the antennas.  Fibre might be useful for radar video, where the antenna is a long way from the control room.
Examples: https://www.etlsystems.com/catalogue/rack-systems/rf-over-fibre

No ideas about voice multiplexed over cables. Hopefully other people can help here.

Comtech tech support are helpful and I suggest you contact them about the purpose of and how to use Memotec Netperformer equipment. See https://www.comtechefdata.com/support/docs/memotec-netperformer-series

If it involves VoIP, I would recommend a substantial investment in trustworthy staff with IT security skills to avoid the system being hacked.

iDirect/SCPC is a continuous digital system, with digital input and outputs. See: https://www.idirect.net/product-directory/

Eric.