current v 2 is applied across shield 80 coaxial insulator 90a and outer armor 84 and direct current voltage v 3 on inner conductor 70 with outer armor 84 as the return path referring to fig2 the pulses e 9 and conductor 70 of cable 72 are provided by slip rings 105 to capacitor 110 while the return path for pulses e 9 is provided by shield 80 of cable 72 through slip rings 105 and capacitor 112 a high voltage power supply 115 provides voltage v 3 through a current limiting resistor 107 and slip rings 105 to conductor 70 of cable 72 capacitor 110 blocks voltage v 3 while passing pulses e 9 a low voltage power supply 116 provides voltage e 2 to shield 80 of cable 72 through slip rings 105 capacitor 112 blocks voltage v 2 while providing a return path for pulses e 9 a resistor 113 connects capacitor 110 to capacitor 112 and pulses e 9 are developed across resistor 113 amplifiers 120 121 and 122 resistors 125 126 and 127 and diodes 130 131 form a pulse separation circuit which separate the positive pulses e 9 from the negative pulses e 9 appearing across resistor 113 resistors 125 126 and 127 have the same resistance value when a positive pulse e 9 is applied through resistor 125 to amplifier 120 a positive pulse e 15 appears at the output of amplifier 120 causing diode 131 to have a very low forward impedance so that the effective gain of amplifier 120 is the ratio of the resistance value of resistor 127 to.