The Antenna Array consists of two rather independent items, the e-field or voltage antenna, and the b-field or magnetic antenna.  For convenience in the prototype locators, the two antennas are combined into a single structure.  If necessary, however, they can be separated by up to 100 feet.  If separated, then it is more important to place the e-field antenna in an elevated position. Also, separation will require a circuit board and weatherproof enclosure near each antenna.

    There is great latitude in the manner in which the Array is constructed, so long as a few basic principles are followed.  Most important is that the Array must be able to withstand the ravages of weather and time.  For one housetop installation, a decorative cupola, constructed entirely of nonconducting material, supports and contains the Array.  At the other esthetic extreme is the rugged but unsightly PVC pipe framework atop the Meteorology Department at Penn State.  Any nonconducting structure that will support the two antennas in a dimensionally stable manner will serve.  PVC pipe is easy to use, weatherproof, robust and provides good electrical insulation.  The upper, ungrounded voltage antenna plate, made of galvanized hardware clothe (do not use aluminum screening) must be reliably insulated under rain or shine conditions from all conductors and ground.  Further, the plate should be positioned at least a few inches above the top of the loops.  The lower, grounded plate requires no insulation and can serve as a platform for holding the electronic circuits box.  The b-field antennas can be made from a variety of coaxial cables and should be accurately constructed.  If cable impedance other than 75 ohms is used, then the 75-ohm terminating resistors shown on the circuit diagram should be adjusted accordingly.  Slightly higher signal strengths will be obtained from higher impedance coax.  It is essential that the areas of the two loops be identical and that they be precisely oriented in the north-south and east-west planes, respectively.  The exact (but identical) area of the loops is not critical but does determine the loop antenna sensitivity (see below), which is directly proportional to the loop areas.

   Since the prototype systems were installed in 1997, we have found that the antenna array is significantly larger than necessary. From equation (2) on page 6 of the GP-1 System section,

   Similarly, the e-field antenna acquires a signal far larger than needed, particularly if installed substantially higher than 10 meters. This antenna, whose dimensions are small compared with the e-field signal wavelength, looks like a capacitor, Ca, whose value is proportional to its area. The net signal at the input, e, to the source follower, Q6, is proportional to the ratio of Ca to (Ca + Ci),

   The signal voltage at the e-field antenna depends on the electric field in volts per meter as given by equation (1) on page 3 of the GP-1 System discussion:

    An aluminum box encloses the circuit board and supports the several connectors.  A 5 x 7 x 3 inch box with a cover cap (Mouser #537-573 and #537-572C) provides plenty of room for all components.  A UHF female, SO-239, connector is placed in the center of the four 3-inch-high sides of the box for loop antenna connectors J5 - J8 (Circuit Diagram).  It is best to place the North loop connector, J5, on one long side of the box.  Looking down on the open face of the box, next place the East connector, J7, on the clockwise, short side; the South connector, J6, on the other long side; and the West connector, J8, on the remaining short side.  A pair of feed-through binding posts, placed on the South box side and to the east of J6 (Antenna Array), make the connector (J0) for the voltage antenna lead wire and ground connection to the grounded antenna plate.  A simple spark gap should be fabricated from two short stiff wires and placed outside the box near J0.  File points on the two wire ends and space them about a 1/32-inch apart.  Since the box is 2 inches longer than it is wide, cut the NS loop coax cables 2 inches longer than the EW loop cable.  Remove about an inch of the shield braid from the center of each cable.  Reinforce and weatherproof the gap with either shrink tubing or vinyl tape. To complete the loop cables, place PL-259 plugs on each end. The three signal output connectors, J2, J3, and J4, also SO-239s, are placed along the North side of the box to either side of J5, along with a 5-pin female DIN connector, J1.

    Bolt four 3-lug terminal strips to the bottom of the box, each 1-1/2 inches out from the box center and on lines between J5 - J6 and J7 - J8.  Connect one lug of each strip to its adjacent loop antenna connector.  Ground one of the remaining lugs and then solder the three components, a 220k resistor, a 75-ohm resistor and a 1uF film capacitor, at each strip as shown on the circuit diagram. These components properly terminate the loop antennas and provide high-pass filtering for 60 Hz noise.  Clip the leads of a 470-ohm, 2-watt carbon resistor, to about 1/2 inch and solder one lead to the inner lug of J0.  The other end of the resistor will connect by way of a flying lead to the Ant pad on the circuit board.  All remaining wiring of the box will be done with flying leads from the circuit board after bench testing.

    A circuit board is available for the Preamplifiers-Integrators from FAR Circuits. See the References section for details. If you prefer to fabricate your own board, then a suggested procedure is described in the Test Signal Source section. In either case it is best to solder all jumper wires in place, before installing other components.  While two-sided boards could have been designed, their fabrication is more difficult than the single-sided variety.  Further, the required addition of via connections between the two sides is at least as tedious as the placement of jumpers required of the single-sided practice.  Jumper placement goes most quickly by using #20 or #22 bare solid wire and insulating sleeving.  The sleeving is first cut to the proper length, a bit longer piece of wire inserted in the sleeving, and then the wire ends are inserted in the circuit board holes and soldered.  This approach proceeds much more quickly than attempting to strip ends from short lengths of insulated wire and having the correct jumper length result.  When all jumpers are in place, the remainder of the board is populated with the circuit components.  Use of integrated circuit sockets is strongly recommended.  When installing the several polarized components (diodes, tantalum capacitors, transistors, and integrated circuits), be careful that they are oriented in the proper direction.

    The values of capacitors C6 and C5 (upper left on the circuit board) determine the normal and computer-controlled attenuated sensitivity of the e-field pathway and may require adjustment with experience.  Generally, the higher the Antenna Array is installed, the greater the attenuation (and larger the capacitance) that is required.  For a single-story rooftop installation and the prototype e-field antenna, C6 should be from 100 to 360pF and C5 from 470 to 820pF.  For very high installations, such as on top of an eight-story building, C6 might range from 1000 to 2000pF and C5 from 2000 to 4700pF.  Be aware that far more performance problems arise from having too much e-field sensitivity, due to overload and premature triggering, than from having too little.

    Board wiring is completed by connecting generous-length flying leads of insulated wire to the pads that ultimately connect to external components.  All leads should emerge from the component side of the board except the Ant (E-field in) and the E and S input wires, which should emerge from the solder side. The use of various wire colors will simplify keeping track of the function of each lead.  When installed after testing, the board will be held with small angle brackets to stand upright from the center of the box bottom and canted about 45 degrees along the northeast to southwest plane.  The component side of the board should face northwest.

    Preliminary testing of the circuit board is best done before installing the board in its box.  After careful inspection for correct wiring, particularly polarized component placement, look for solder splashes between the copper traces.  When all looks well and before inserting any ICs into their sockets, check the resistance from ground to both the +12 and -12 volt (rail) power leads.  Each should show a resistance greater than 100k; otherwise there is a wiring fault.  Next, connect a +12 and -12 volt test power supply to the board in a manner that allows current monitoring.  Only 13 to 14 milliamperes (mA) should flow in either +12 or -12 volt rail.  Higher current indicates a wiring fault; most likely a tantalum capacitor is installed in the wrong polarity between a rail and ground.  As the last static test, install the ICs, one at a time, and check rail currents.  The currents should increase only a few mA as each new IC is installed.  With all ICs in place, both the +12 rail and -12 rail current will be about 44 mA.  If no smoke is seen and no components are more than slightly warm, then signal testing can proceed.

    The Test Signal Source, with its temporary auxiliary loop, and an oscilloscope are required for the following tests.  Tack-solder one end of four 75-ohm resistors to the ground foil of the circuit board and connect the ends of the N, S, E, and W flying leads to the other end of each resistor.  Tack-solder three 100-ohm resistors to the ground foil and solder the leads from NS, EW, and E-field out to the other ends of each resistor.  These temporary connections will properly terminate the three signal channels for the following tests.

   Next perform the EW Preamplifier/Integrator test.  Note that the input wave shape is the same as dB/dt that was obtained when the Source was tested.  The EW output shows the Source magnetic field magnitude, B.  Repeat the test for the NS Preamplifier/Integrator.

    The E-field voltage follower test uses the Source E-field output as the test signal.  The voltage follower input and output waveshapes are identical, but there is a small signal level attenuation.  The exact magnitude of both the input and output signals will depend on the value of C6  (100pF in the example shown).  C6 provides fixed attenuation that must be determined at each installation.  As noted above, generally the attenuation must be made larger with increasing e-field antenna height.  (Note that if C6 is made larger than 1000pF, then Signal Source E-output switch, S5, must be in the Short position for adequate signal strength.)

   A fast sweep on a two-channel oscilloscope will reveal about a 0.2 microsecond lag of both magnetic field outputs (NS and EW) behind the E-field output.  This lag is produced by the RC stabilizing network (270 ohms, 330pF) across the input terminals of U1, U2, U3, and U4.  These lags are fortuitous in later timing in the Signal Gate and Track-Hold boards.

    The remaining procedure is the adjustment of the NS and EW Integrator common-mode balance trim pots, P1 and P2. To perform this adjustment, remove the four 75-ohm resistors that were tacked in place earlier.  Next, temporarily solder together the E lead to the W lead and the N lead to the S lead.  To provide a common mode signal to the EW Preamplifier/Integrator, tack solder one end of two or three feet of insulated wire to the E and W input junction; the other wire end remains unconnected.  This will capacity-couple a 60-Hz input signal from stray fields in the area.  With the oscilloscope connected to the EW output, carefully adjust P2 for a sharp null in output.  Slight misadjustment, on either side of the null, will produce a large 60-Hz output.  When the best null has been achieved, repeat the above for the NS Preamplifier/Integrator by adjusting P1.

    When all the tests and adjustments have been successfully completed, remove the remaining three temporary 100-ohm resistors and separate the temporary E to W and N to S lead connections.  The circuit board can now be installed in the metal box and all flying leads joined to their appropriate connectors, as shown in the circuit diagram.  Lead dress is not critical but avoid excessive lengths of the signal-carrying wires.  The Ant (E-in) lead will go to the free end of the 470-ohm resistor previously connected to J0.  N, S, E, and W leads go to their nearby 3-lug strips.  The DC power and relay leads connect to J1, and the signal output leads to J2, J3, and J4.  When all the installation wiring is complete, make one more ohmmeter check of both rails to ground.  As earlier, resistance greater than 100k should be found.  The metal lid to the enclosure box can now be fastened in place.

    The preamplifiers/integrators box can now be installed at the base of the Antenna Array.  Connect the four loop PL-259 plugs to the appropriate J5, J6, J7, and J8 connector.  A permanent ground wire should join the lower voltage field antenna plate to the ground terminal of the Preamplifier input.  The lower plate must also be securely grounded to a ground rod or building steel framework.  A drop-down wire from the upper E-field antenna plate will be connected to J0 after testing with the Signal Source, below. It is important that this drop-down wire be brought to J0 straight down the central axis of the loop pair so as not to induce an e-field-generated current into the loops. The box loop connectors should be slightly elevated above the lower horizontal loop arms to prevent rain water from running into the connectors.  Fasten the box firmly to the Array base framework to prevent movement in high wind.  Place PL-259 plugs on each end of three coaxial cables and a 5-pin male DIN connector on each end of a 4-wire power cable of sufficient length to reach the site of the Interface and the PC.  Cable length is not critical; up to 200 feet has proven satisfactory. Mark each end of the coaxial cables as to function. To minimize field distortion, bring the connecting cables away from the Array in a vertical direction as far as possible.  Long, horizontal runs from the Array base have produced serious bearing anomalies. Finally, place an inverted plastic tub over the box to ward off rain and snow.

    Final testing of the Antenna Array is performed using the Test Signal Source and an oscilloscope.  First, prepare three temporary terminations for the three signal cables using SO-239 connectors.  Solder one lead of a 1uF film capacitor to the center terminal of each connector and the other lead to a 100-ohm resistor.  The other lead of the resistor is then soldered to the connector cases.  The oscilloscope probes are then connected across the resistors.  These terminations duplicate the signal input loads that will be provided later by the Interface.  Also, prepare a temporary female 5-pin DIN connector to supply DC power to the Array.   Before applying power to the Array, make one more ohmmeter test of each rail to ground to make sure no fault occurs in the power cable.  If all looks well, then apply power to the Array and find about the same rail currents (44 mA) as in the earlier circuit board test.

    Place the Test Signal Source inside the crossed loops of the Array.  It can simply rest on top of the box or plastic tub cover.  Connect the Source E-field ground output terminal to the grounded antenna plate and the Source E-out terminal to J0.  Turn the Source power on and set it for NR, Hi, mono, and 100pf (unless C6 exceeds 1000pF, then use Short) output.  Connect the oscilloscope to the terminating 100-ohm resistor of the E-cable.  The signal seen should be similar to that shown.  Switching the Source to Lo should produce a similar waveform but of peak magnitude about 400 millivolts (mV) (depending on the value of C6).  Using PR and biph Source settings should also produce appropriate waveshapes.  Restore the Source to the original NR, Hi, mono output and orient it so the front panel faces the Array northeast.  Connect the oscilloscope to the EW terminating resistor and then to the NS terminating resistor.  Waveforms similar to those shown should be seen.  That these signals really represent the EW and NS vectors of a field from the northeast is illustrated by an XY display of the signal pair.  This figure simulates what will occur when the system is completed by adding the Interface and PC.  To further confirm the magnetic field performance, reorient the Source and note the EW and NS signal magnitudes and polarities such as illustrated by the west-southwest test waveforms and vector plots.  When the above tests are completed satisfactorily, the Array can be permanently installed in its chosen site. Remove the Source and connect the drop-down lead from the upper voltage field antenna plate to J0. From time to time, however, the Array will require access for testing and, possibly, altering the values of C6 and C5.

    Some performance of the Array can be observed by simply connecting an oscilloscope to the signal cables with their temporary terminations.  With a 'scope in the XY-mode, directional vectors may be observed to man-made sources, such as nearby AM broadcast stations and sporadically-switched AC powered items.  It is possible that nearby lightning strokes may be seen if they are very frequent.  However, do not be surprised if they are rarely seen, as their duration is so brief that they are barely visible at best.  There will also be a 180-degree uncertainty concerning the true direction because E-field polarity determination is not yet available.