Electronic roll-a-long switch

An electronic roll-a-long switch for use in a seismic exploration system, said system including N receiver points for receiving signals from seismic detectors, which receiver points are sequentially numbered and located at spaced intervals along the earth's surface, and a recording system having channels for recording seismic data, comprising:

• N/2 input channels for receiving signals from a group of N/2 receiver points, each said input channel including selection circuitry for individually selecting one of two receiver points for connection to a designated channel, the two said receiver points for each designated channel being spaced N/2 receiver points apart, and a multiplexer for time multiplexing the signal on each input channel to a signal bus;
• and timing and control apparatus including circuitry:
• (a) for operating the multiplexer during each channel sample time of a record interval time to select a group of M channels from the N/2 input channels to be data channels and to connect said group of M data channels to the signal bus in a sequential order corresponding to the sequential numbers of the receiver points from which group of data channels were selected;
• and
• (b) for operating the selection circuitry to change the group N/2 receiver points which are connected to the input channels during a subsequent interval time.