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?