‰ NOW 35 WPM ‰ TEXT IS FROM DECEMBER 2013 QST PAGE 49‰ HANDS ON RADIO H. WARD SILVER, N0AX, N0AX ARRL. ORG EXPERIMENT 131 COAX TO OPEN WIRE LINE BALUN I RECENTLY DESIGNED SOME EXTENDED DOUBLE ZEPP EDZ ANTENNAS THAT PRESENT A REASONABLE SWR ON 14 AND 21 MHZ. THE DESIGN USES A SPECIFIC LENGTH OF 450 LADDER LINE, RESULTING IN AN SWR OF LESS THAN 2 1 AT THE END OF THE LADDER LINE ON BOTH BANDS. SINCE THAT LENGTH WAS TOO SHORT TO REACH THE SHACK, I CHOSE TO TRANSITION FROM THE 450 LINE TO 50 COAXIAL CABLE. THE EDZ DESIGN WILL BE PRESENTED IN A FUTURE COLUMN OR ARTICLE. ONE CAN JUST CONNECT THE COAX TO THE LADDER LINE AND HOPE FOR THE BEST IT MIGHT WORK, AS SOME DESIGNS FOR MULTIBAND ANTENNAS WILL FUNCTION THAT WAY. UNFORTUNATELY, THE OUTSIDE OF THE COAX SHIELD IS ALSO CONNECTED AT THE JUNCTION OF THE TWO FEED LINES, CREATING A COMMON MODE CURRENT PATH WITH IMPEDANCE DEPENDING ON THE LENGTH OF THE COAX AND THE OPERATING FREQUENCY. THE BASIC IDEA IS EXPLAINED IN ROY LEWALLENS, W7EL, CLASSIC ARTICLE BALUNS WHAT THEY DO, AT WWW. EZNEC. COM/ AMATEUR/ ARTICLES/ BALUNS. PDF. IF YOU HAVENT READ IT, THIS WOULD BE A GOOD TIME TO DO SO. THE CASE FOR USING A BALUN ROYS ARTICLE SHOWS WHY A CURRENT OR CHOKE BALUN IS NEEDED AT THE TRANSITION FROM THE COAX TO A DIPOLE WITH THE WIRES AT RIGHT ANGLES TO THE COAX. WHAT IF INSTEAD OF A DIPOLE, THE COAX IS CONNECTED TO LADDER LINE? IS A BALUN STILL NECESSARY? IN TRANSMISSION LINES, THE CONDUCTORS ARE ‰ END OF 35 WPM TEXT ‰ QST DE W1AW ƒ