A communication system such as an OFDM or DMT system has nodes which are allowed to transmit continuously on one or just a few of the sysiem’s frequency sub-channels, while the other nodes avoid putting any signal into those sub-channels. According to one embodiment, the embedded phase noise detection system can include an active delay line cell, a phase shifter, and a phase detector. , enzyme activity and catalytic or reactive molecule activity. The left and right main seed hoppers are transversely separated from one another by a longitudinally extending gap located along the longitudinal centerline of the seeding machine.