Output waveshapes from the Signal Source with switches set to Hi-, NR-, Mono-, and 100pf-positions (upper figure) or to Hi-, NR-, Biph-, and 100pf-positions (lower figure), as seen on a 2-channel oscilloscope. The waves in the upper figure approximate a negative return stroke within 100 km, and the waves in the lower figure approximate a negative intracloud stroke. Vertical sensitivity for each 'scope channel (CH1 and CH2) is as indicated.  Sweep rate is 2.5 microseconds per large division.  E is the voltage field signal terminated by a 100pF capacitor. The signal dB/dt is obtained from a temporary 1-turn loop of wire taped to the pipe square. The active terminal of the 'scope probe is connected to the 1-turn loop end adjacent (hi end) to the front panel and the probe ground terminal to the other (low end) end of the loop.  The waveshape obtained is the rate of change of the magnetic field generated.  When integrated in the Antenna Array magnetic field circuits, the waveshape,  B,  will be identical to that of the E-field, above.  Both E and dB/dt waves are inverted when S2 is in the PR position to simulate a positive return stroke in the upper figure and a positive intracloud stroke in the lower figure.  When S3 is switched to Lo, a stroke beyond 200 km is simulated.