Abstract: A baseband signal is spectrally efficiently transmitted on a broadband transmission medium by inserting gaps in packets of digital data transmitted in a modulated first radio frequency carrier. The transmitted packets of data are received by demodulating the modulated first radio frequency carrier, and the gap is monitored for the presence of digital data thus indicating a collision of simultaneously transmitted packets of digital data. A seed of arbitrary digital bits are used in scrambling each packet of digital data and is transmitted with the packet of data for use in descrambling the data. In retransmitting the packet of data the seed is included. The originally transmitting node receives the retransmitted packet and compares the retransmitted seed with the originally transmitted seed for detecting an error in retransmission.