In the Spring of 2001 this Antenna Array Signal Simulator was replaced by an improved version, the Lightning Stroke Simulator. This subsection remains for reference purposes and we recommend that only the Lightning Stroke Simulator be constructed. No circuit board is available from FAR Circuits.
The Array Simulator generates its waveforms in a similar manner to that done by the Test Signal Source, and so they have a similar shape. However, their output circuits differ to be suitable for driving the Interface directly.
The Antenna Simulator (Simulator), when used in place of the Antenna Array, can simulate near- and far-stroke signals from eight directions: north, northeast, east, etc., as negative return strokes, positive return strokes, or intracloud strokes. Thus, all important performance characteristics of the Interface circuits and the software can be tested.
The Simulator circuit board is etched, and the jumpers and components are placed as described in the Test Signal Source and Antenna Array construction. Before installing the completed board in its cabinet, make the same preliminary tests as were done on earlier boards. Prior to installing the ICs, the positive and negative rail resistance to ground should be about 10k to 12k. When the board is connected to a power supply, the currents should be about 7 to 10 mA in each rail. Much lower resistances or higher currents suggest a wiring error. When these tests are successful, all ICs can be plugged into their sockets. Once again, measure the power supply currents and find about 60 mA in the +12 V rail and about 40 mA in the -12 V rail. Upon successful completion of these preliminary tests, the circuit board can be installed in its cabinet and wired to the external components.
The circuit board, power supply, and panel components fit conveniently in a 7.3 x 6.3 x 2.8 inch metal cabinet such as Jameco Part No. 11949. The lower, U-shaped portion of the cabinet that forms the front and rear panels is lightweight aluminum that requires user-installed angle brackets attached to the steel top for improved stiffness. The suggested power supply is placed in the rear, while the circuit board is toward the front. Since the circuit board is wider (3.05") than the cabinet is high (2.8"), it should be fastened to the cabinet bottom with 45-degree angle brackets so the board slants with its top edge toward the rear. The component side should face the front panel. All switches and output jacks are mounted on the front panel. The flying leads from the board are connected to the panel components and power supply. Although lead dress is not critical, enough slack should be left in each wire so the board can be examined on both sides, if necessary. When all wiring is complete, make one more rail current check, as above. If all is well, then the same currents (60 and 40 mA) should be found. Temporarily tack-solder 100-ohm terminating resistors across J1, J2, and J3.
Adjustment of the trim pots, P1 through P5, is aided by an oscilloscope with its sweep set to about 2.5 microseconds per cm. The following description assumes use of a single-channel 'scope. However, waveforms shown were obtained using a two-channel instrument. Connect the 'scope to the terminating resistor across J1 (E-out), with the switches all set as in the Monophasic E and NS output test. Switch the Simulator power on and see waveforms similar to E. Switch S2 to the Biphasic-position. With a small screwdriver, rotate P1 over its full range. When fully clockwise (CW), note a minimum overshoot similar to that shown in the Monophasic E and NS output test; when fully counterclockwise (CCW), note a maximum overshoot. For most purposes, with S2 in the Biphasic-position, near maximum overshoot, with P1 near the extreme CCW position, is best. With all switches back in their initial positions and the 'scope still connected to the J1 terminating resistor, adjust the 'scope sensitivity so that, with the E-field waveform centered, the peak reaches the top screen scale mark. Next, switch S3 to the inv-position and note that the waveform inverts and the peak is near the bottom screen scale mark. Adjust P2 (near its center excursion) until the peak is exactly on the bottom scale mark. Switch S3 back and forth between the norm- and inv-positions, and make any further fine adjustment of P2 until the two magnitudes are identical. This process sets the gain of U5 to exact unity. For the P3 adjustment to calibrate the E output magnitude, restore all switches and set the 'scope vertical sensitivity to 2 volts full scale. With S4 in the max-position, adjust P3 so that the waveform peak is at the top scale mark when S3 in the norm-position and at the bottom scale mark when S3 is in the inv-position. Switch S4 to min and observe that the peaks show close to +0.5 and -0.5 volt when S3 is switched between norm and inv. The last adjustments calibrate the NS and EW output levels. Connect the 'scope to the terminating resistor across J2 (NS) and adjust its vertical sensitivity to 2 volts full scale. With S7 in the max-position, adjust P4 until the peaks just reach the top and bottom scale marks when S5 is switched between the N- and S-positions. Similarly, connect the 'scope to the terminating resistor across J3 (EW) and adjust P5 for the exact same peak excursions. This completes the trim pot adjustments.
As a final check on the Simulator performance, note that the output waveforms are very close to those shown for E and NS monophasic output simulating a negative return stroke, E and NS biphasic output simulating an intracloud stroke, NS and EW monophasic output simulating a negative return stroke from the northwest and NS and EW monophasic output simulating a negative return stroke from the southeast. These last two pairs of waveforms show two of the possible eight directions that can be simulated. The cabinet cover can be fastened in place and the Simulator set aside for later use.