The disclosure relates to a communications system having a transmitter and receiver connected via a transmission line. An example communications receiver (202) comprises: a pair of input connections (211, 212) for connecting to a transmission line (203); a termination resistance (213) equal to a characteristic impedance (Zc) of the transmission line (203); an air core transformer (205) having an input coil (206) connected to the pair of input connections (211, 212) via the termination resistance (213); and a comparator circuit (208) connected to an output coil (207) of the air core transformer (205), the comparator circuit (208) configured to provide an output signal (504) responsive to detection of voltage pulses across the output coil (207).