Where does the ground of the audio path go in this schematic?
If the schematic doesn't show a separate audio signal ground, then the audio input ground is clearly meant to be connected to chassis ground. The power supply ground is also not shown, which means that it too should be tied to chassis ground. All the ground symbols in the schematic are chassis ground, rather than earth ground.
Since the circuit is an RF circuit, you should probably build it in a shielded enclosure (aka chassis), which would be the chassis ground. The RF input and output connectors should be RF coaxial connectors, grounded to the chassis of course. The enclosure should be connected to the station ground.
(A comment with essentially the same information as this answer was posted several days before. This answer was posted mainly so that the question officially has an answer, in the hope that the question won't keep popping up again and again on the "home" page.)