At its simplest, radio is a direct transmitter to receiver medium. However, the physics of radio propagation can affect distance and reliability. Radio repeaters can mitigate these issues, and networking of repeaters allows radio comms over a large geographical areas. Repeaters in different geographical areas can be interconnected via networks to provide regional comms.
Using a repeater is similar to a party line. Everybody is communicating in a shared space. Different repeaters can provide different shared spaces, akin to channels in IRC or chat rooms.
A digital voice hub is a like a virtual repeater. It is a shared space where participants can talk.
The RadioFreqs.space voice hub can currently be accessed by amateur radio operators using one of the following:
