What Are They? Balun = Balanced Unbalanced Current - forces symmetrical current on terminals Current determines radiation pattern Voltage – forces symmetrical voltage on terminals Less efficient, less common Unun = Unbalanced Unbalanced Transmission line transformers What Is Balanced vs Unbalanced? Balanced Load – ladder line Unbalanced Load - coax I1 I2 I3* *I3 = common-mode current is greatest at multiple of ½ λ Types of Baluns Voltage or Current Transformer Torroid core Ferrite Powdered Iron Rod core Current Choke Air Wound Scramble Form Bead Torroid Types of Baluns Air Core – scramble wound Choke - Bead Types of Baluns Torroid– ferrite Choke - Bead Types of Baluns/Ununs Torroid– ferrite L-R: 1:1 current balun, 4:1 voltage balun, 1:1 current unun Yaesu FC-40 AMU (unun) Uses for Baluns and Ununs Balun OCF dipole Yagi Windom G5RV Unun Vertical Long wire Loop Uses for Baluns and Ununs Uses for Baluns and Ununs The Project HF antenna capable of multi-band operation Off-Center-Fed (OCF) dipole looked good – tuner not required OCF presents 200 Ω impedance Needed a 4:1 current balun to transform 200Ω to 50 Ω Articles by Jerry Sevick, W2FMI (SK) Amidon Associates The Project W2FMI 4:1 –HBM200 Balun FT-240-K ferrite core two 14 AWG bifilar windings, 100-ohms each 15-mil teflon sleeve 1MHz – 50MHz range 2KW continuous 4KW peak 98% efficiency Finished Product Test Results* SWR Band Frequency 1.1 160 1.9 MHz 1.1 80 3.9 1.1 40 7.2 1.2 20 14.2 1.3 17 18.1 1.4 12 24.9 1.5 10 29 1.7 6 52.5 * Two 100 Ω resistors in series used to simulate load Next Step 1/3 4:1 balun 2/3 coax 1:1 line isolator Yaesu 897D Sources “Baluns: What They Do And How They Do It”, Roy Lewallen W7EL, ARRL Antenna Compendium, Vol. 1. “Transmission Line Transformers Handbook”, Jerry Sevick W2FMI. “The ARRL Antenna Book For Radio Communications”, 22d Edition, ARRL. “The ARRL Handbook For Radio Communications”, 88th Edition, ARRL. “More On The 1:1 Balun”, Jerry Sevick W2FMI, CQ, April 1994 Amidon Associates, http://www.amidoncorp.com Palomar Engineering, http://www.palomar-engineers.com Questions?