‰ NOW 40 WPM ‰ TEXT IS FROM JUNE 2015 QST PAGE 63‰ PROBLEMS. MIKE SUGGESTS THAT RFI MITIGATION DETAILS BE WORKED OUT IN ADVANCE BEFORE THE BOARD SIGNS A CONTRACT. IF THERE IS HARMFUL INTERFERENCE TO LICENSED OPERATORS, INCLUDING AMATEUR RADIO OPERATORS, THE RULES PLACE THE BURDEN ON THE DEVICE OPERATOR YOUR CONDO BOARD TO FIX THE PROBLEM. LETS HOPE IT DOESNT GET THAT FAR. ONE SUGGESTION THAT MIGHT HELP HEAD OFF PROBLEMS WOULD BE TO REQUEST THAT THE BOARD ASK BIDDERS TO SUPPLY REFERENCE ACCOUNTS THAT USE THE PROPOSED SHIELD IS OF THE SAME MAGNITUDE, BUT OF THE OPPOSITE PHASE, AS THAT ON THE CENTER CONDUCTOR. IN THIS CASE, THE ANTENNA HAS NO CLUE AS TO WHICH SIDE IS CONNECTED TO THE SHIELD. EVEN IF THERE IS NO COMMON MODE CHOKE OR BALUN AND SOME CURRENT FLOWS DOWN THE OUTSIDE OF THE SHIELD, NEITHER THE INSIDE, NOR THE OUTSIDE, OF THE ANTENNA END OF THE COAX SHIELD IS GENERALLY AT GROUND POTENTIAL. SO THE HALF DIPOLE CONNECTED TO THE SHIELD IS JUST AS MUCH A PART OF THE RADIATING ANTENNA AS THE HALF CONNECTED TO THE INNER CONDUCTOR. Q ASKS IN THE EARLY 1960S, MY HIGH SCHOOL HAM BUDDIES AND I WERE HANGING OUT ON 40 METER PHONE ON FRIDAY AND SATURDAY NIGHTS, RAGCHEWING. WE SPENT MANY ENJOYABLE HOURS ON 40 METER AM WITH OUR 40 TO 100 W OUTPUT RIGS OF THE PERIOD. WE WERE ALL WITHIN 12 TO 15 MILES OF EACH OTHER, WERE USING DIPOLES OR SIMPLE VERTICALS, AND SIGNALS WERE ALL S 9. FAST FORWARD 50 SOME YEARS. WE ARE ALL BACK ON THE AIR NOW, AND RETIRED AFTER BUILDING BUSINESSES AND RAISING FAMILIES. WE HAVE BALUNS ON OUR DIPOLES, GOOD MATCHING AT THE BASE OF OUR VERTICALS, STATE OF THE ART 100 W SSB RIGS AND, ALTHOUGH IN HOMES AND NEIGHBORHOODS SOMEWHAT DIFFERENT FROM WELL, A DIPOLE IS AN INHERENTLY BALANCED ANTENNA, AND EACH SIDE IS EQUIVALENT. WE GENERALLY THINK OF A COUNTERPOISE AS A METALLIC STRUCTURE EITHER ACTING AS AN ARTIFICIAL GROUND, OR SOMETIMES ALSO ACTING AS ONE PLATE OF A CAPACITOR COUPLING TO THE GROUND UNDERNEATH. A WAVE ANTENNA, SUCH AS A GROUND PLANE, MONOPOLE, OR MARCONI END FED WIRE, DEPENDS ON THE GROUND SYSTEM, OR COUNTERPOISE TO ACT AS THE OTHER HALF OF THE ANTENNA. THE ANTENNAS RADIATION OCCURS BECAUSE OF THE TIME VARYING FIELD SET UP BETWEEN THE MONOPOLE AND THE ASSOCIATED GROUND SYSTEM. IN A DIPOLE, THE RADIATION OCCURS BECAUSE OF THE TIME VARYING ELECTROMAGNETIC FIELD BETWEEN THE TWO HALVES OF THE DIPOLE. SO IN A SENSE, IN ALL CASES, THE ANTENNA ITSELF DOESNT RADIATE AT ALL IT IS THE FIELDS ESTABLISHED BETWEEN THE PARTS OF THE ANTENNA THAT DO THE RADIATING, WHILE THE ANTENNA ITSELF SETS UP THE FIELDS. IN A DIPOLE, EACH SIDE IS EQUALLY INVOLVED IN THE PROCESS. PERHAPS YOUR FRIEND IS CONFUSED BY THE FACT THAT THE COAX SHIELD IS OFTEN CONNECTED TO ONE SIDE OF THE DIPOLE AND AT THE STATION END IS USUALLY CONNECTED TO GROUND. WHILE BOTH ENDS OF THE SHIELD ARE AT A SIMILAR DC POTENTIAL, IF THE CABLE IS OF ANY LENGTH THE ANTENNA END IS AT A VERY DIFFERENT RF POTENTIAL. IF THE OUTSIDE OF THE SHIELD IS PROPERLY DECOUPLED TO AVOID COMMON MODE CURRENT, THE RF VOLTAGE ON THE ANTENNA END OF THE COAX ‰ END OF 40 WPM TEXT ‰ QST DE W1AW ƒ