[[File:PROP1.png|thumb|300px|[[Propagation Module]]'s Base Set dialog]]
Transmitters and receivers are more complicated source and observables representing a observable types that can be used to model more realistic communication linklinks. A conventional urban propagation scene can be set up using a transmitter source and an array of receivers. In order to tie up transmitters and receivers with CAD objects in the project workspace, [[EM.CubeTerrano]] uses point objects to define transmitters and receivers. These point objects represent the base of the location of transmitters and receivers in the computational domain. Hence, they are grouped together as "Base Sets". You can easily interchange the role of transmitters and receivers in a scene by switching their associated bases. The usefulness of concept of base sets will become apparent later when you place transmitters or receivers on an irregular terrain and adjust their elevation.
To create a new base set, right click on the '''Base Sets''' item of Navigation Tree and select '''Insert Base Set...''' A dialog for setting up the Base Set properties opens up.