Abstract: A hybrid fiber/coax digital data transmission system in which data from a plurality of subscribers are transmitted upstream to a headend demodulator in a series of data bursts. The headend demodulator acquires and synchronizes a data burst by detecting a BPSK preamble having a repetitive one and zero pattern (10101010101000). The pattern is detected by integrating clock energy in an envelope of a preamble length transmission and using the last three symbols (0,0,0) as a frame marker after differential decoding. Noise in the system is periodically measured by detecting an empty burst placed periodically in the data stream. A first-in, first-out (FIFO) memory allows closer spacing for the data bursts by permitting asynchronous received and output clocks.