the control input circuit means 40 is tse and makes a state transition to the receive mode when the output of the input control circuit means is rse therefore if z1 u2260 z2 z1 gt z2 z1 z1 39 z3 z3 39 and z2 z2 39 z4 z4 39 a a 39 gain of the comparators 46 48 then the magnitude of the signal tse is given by the equation equ1 tse a ts z1 z2 rs and the magnitude of the signal rse is given by the equation equ2 rse a rs z1 z2 ts thus for the transmit signal to overtake the receive signal and generate a signal tse the transmit signal must overcome the hysteresis z1 z2 and for the receive signal to overtake the transmit signal and generate a signal rse the receive signal must overcome the hysteresis z1 z2 the ratio of the impedances z1 z2 then is the hysteresis level with all unwanted noise signals substantially cancelled out equations 1 and 2 are graphically illustrated in fig3 to point out the overtake level z1 z2 which is represented as the separation between the transition lines this separation between transitions or hysteresis may be easily narrowed or widened by adjusting the ratio of the impedances z1 z2 referring now to fig4 the transmit peak detector 41 provides a.