This read-only value, in dBm, reports the received gain control setting for the modem's diversity (secondary) antenna path, with -1 indicating the value is unavailable. An admin comparing this to c3gRxMainGainControl can assess whether the diversity antenna is contributing meaningfully to reception or whether it might be disconnected or underperforming, especially relevant to physical antenna installations. For example, if the diversity gain control shows unavailable while the main antenna reports a normal value, the admin might suspect a disconnected or faulty diversity antenna cable.