Transmitter
The transmitter takes in audio data through a Copper Wire, and transmits it to its configured frequency.
Although not required, a core can be placed behind it, with an Antenna structure above it to provide additional range to the transmitter.
Catalysts
Both the receiver and the transmitter require a Catalyst in order to function.
This determines the quality that audio will have upon passing through it,
as well as a unique audio filter depending on the catalyst.
To add a catalyst, simply right click the block while holding the catalyst you want to add, or an empty hand if you want to remove the catalyst.
As of the latest update for Simple Radio, the only catalyst that can be used within receivers and transmitters is Gilded Blackstone.