‰  NOW 40 WPM  ‰  
OF ABOUT 550 KHZ.  A HIGH PASS FILTER MAY BE NECESSARY IF THE ACTIVE DIPOLE
IS TO BE USED ABOVE 2 MHZ IN THE PRESENCE OF STRONG AM BROADCAST STATIONS.
FOR SITUATIONS WITH EXTREMELY LARGE BROADCAST SIGNALS, THE GAIN OF THE
PREAMP MAY BE REDUCED BY INCREASING R102.  WITH THE DIPOLE ELEMENTS MOUNTED
VERTICALLY ABOUT 12 FEET OFF THE GROUND AND SURROUNDED BY TREES, WH2XND
1,036 KILOMETERS FROM HERE, IS REGULARLY SPOTTED ON 136 KHZ WSPR WITH
SIGNAL TO NOISE RATIOS OF 25 DB DURING D

C201 AND C210 PROVIDE COMPENSATION FOR THE CAPACITANCE OF THE CAT5 CABLE ON
THE OP AMP INPUT.  U202 IS A RAIL SPLITTER TO ESTABLISH LOCAL DC GROUND.
THIS RAIL SPLITTER MUST SUPPLY THE DC COMPONENT OF THE OUTPUT SIGNAL FROM
U201.  THE DC SUPPLY VOLTAGE CAN BE ANYTHING FROM ABOUT 0 TO 24 V.  SUPPLY
CURRENT FOR BOTH THE PREAMP AND THE SUMMING AMP TOGETHER IS ABOUT 35 MA.  A
HIGHER SUPPLY VOLTAGE WILL ALLOW THE OP AMP OUTPUTS TO SWING FURTHER
WITHOUT SATURATING ON STRONG LOCAL SIGNALS, BUT IN NO CASE SHOULD THE OP
AMP MAXIMUM RATING OF 24 V BE EXCEEDED.  A SPLIT SUPPLY R5 V TO R12 V CAN
ALSO BE USED, IN WHICH CASE THE RAIL SPLITTER OP AMP CAN BE OMITTED.
CONSTRUCTION  SMALL PRINTED CIRCUIT BOARDS PC BOARDS WERE FABRICATED FOR
THE CIRCUITS AS SHOWN IN FIGURE 4.  OTHERS SHOULD BE ABLE TO MAKE THEIR OWN
BOARDS USING ONE OF THE PROTOTYPING SERVICES SUCH AS EXPRESSPCB.  THE
CIRCUITS CAN ALSO BE BUILT DEAD BUG STYLE ON SMALL PIECES OF COPPER CLAD
BOARD.  THE PREAMP CIRCUIT IS HOUSED IN A 3 4 INCH PVC ELECTRICAL T, SHOWN
IN FIGURE 5.  THE DIPOLE ELEMENTS ARE 1/16 INCH BRAZING RODS APPROXIMATELY
45 CENTIMETERS LONG, HELD IN PLACE BY 1/2 INCH PVC PLUGS THREADED INTO
BUSHINGS THAT ARE GLUED INTO THE ENDS OF THE PVC T.  INSIDE THE T, THE ENDS
OF THE BRAZING RODS ARE CONNECTED TO THE PC BOARD BY SHORT LENGTHS OF THIN
WIRE.  THE HOLES THROUGH THE PVC PLUGS FOR THE DIPOLE ELEMENTS ARE SEALED

WITH FLOWABLE SILICON WINDSHIELD AND GLASS SEALER, AVAILABLE AT MOST AUTO
SUPPLY HOUSES.  THE WHOLE ASSEMBLY IS SUPPORTED BY 3/4 INCH SCHEDULE 80 PVC
FASTENED TO THE STEM OF THE PVC T WITH APPROPRIATE ADAPTERS.  THIS IS IN
TURN FASTENED TO A 1 INCH ELECTRICAL METALLIC TUBING EMT SWEEP SUPPORTED BY
A 10 FOOT LENGTH OF 1 INCH EMT, AS SHOWN IN FIGURE 5.  THE DIPOLE IS
MOUNTED VERTICALLY, MAKING IT OMNIDIRECTIONAL WITH VERTICAL POLARIZATION.
IF IT IS MOUNTED HORIZONTALLY, ADVANTAGE CAN BE TAKEN OF THE DIPOLES
DIRECTIVITY TO NULL UNWANTED NOISE SOURCES.  ALL THREADED CONNECTIONS
SHOULD BE SEALED WITH TEFLON TAPE AND ALL GLUED CONNECTIONS SHOULD BE MADE
UP AS IF THEY ARE TO WITHSTAND WATER PRESSURE.  THIS WILL ENSURE THE
WEATHERPROOF INTEGRITY OF THE HOUSING.  THE SUMMING AMPLIFIER WAS MOUNTED
IN A SMALL BOX FABRICATED FROM SCRAP ALUMINUM, SHOWN IN FIGURE 6.  A SMALL
LINEAR POWER SUPPLY WAS INCLUDED IN THE BOX AS WELL AS A 550 KHZ LOW PASS
FILTER THAT CAN BE SWITCHED OUT FOR RECEPTION OF THE AM BROADCAST BAND AND
HIGHER FREQUENCIES.  THE ACTIVE DIPOLE, SEEN IN FIGURE 7 MOUNTED ON
CONDUIT, CAN ALSO BE POWERED FROM BATTERIES OR AN APPROPRIATE WALL WART,
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ