Baluns and Ununs

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 Current Choke Torroid core Ferrite Powdered Iron Rod core Current Choke Air Wound Scramble Form Bead Torroid

Air Core – scramble wound Types of Baluns Air Core – scramble wound Choke - Bead

Types of Baluns Torroid– ferrite Choke - Bead

L-R: 1:1 current balun, 4:1 voltage balun, 1:1 current unun Types of Baluns/Ununs Torroid– ferrite Yaesu FC-40 AMU (unun) L-R: 1:1 current balun, 4:1 voltage balun, 1:1 current unun

Uses for Baluns and Ununs 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 80 3.9 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 4:1 balun 1/3 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?