1. Baluns and Ununs

2. 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

3. 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

4. Types of Baluns Voltage or Current Transformer Current Choke
Torroid core
Ferrite
Powdered Iron
Rod core
Current Choke
Air Wound
Scramble
Form
Bead
Torroid

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

6. Types of Baluns
Torroid– ferrite
Choke - Bead

7. 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

8. Uses for Baluns and Ununs
OCF dipole
Yagi
Windom
G5RV
Unun
Vertical
Long wire
Loop

9. Uses for Baluns and Ununs

10. Uses for Baluns and Ununs

11. 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

12. The Project

13. 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

14. Finished Product

15. 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

16. Next Step
4:1 balun
1/3
2/3
coax
1:1 line
isolator
Yaesu
897D

17. 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,
Palomar Engineering,

18. Questions?