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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 UnbalancedTransmission line transformers
What Is Balanced vs Unbalanced?Balanced Load – ladder
lineUnbalanced Load - coax
I1
I2 I3*
*I3 = common-mode currentis greatest at multiple of ½ λ
Types of BalunsVoltage or Current Transformer
Torroid core Ferrite Powdered Iron
Rod coreCurrent Choke
Air Wound Scramble Form
BeadTorroid
Types of BalunsAir Core – scramble
woundChoke - Bead
Types of BalunsTorroid– ferrite Choke - Bead
Types of Baluns/UnunsTorroid– ferrite
Yaesu FC-40 AMU (unun)
L-R: 1:1 current balun, 4:1 voltage balun, 1:1 current
unun
Uses for Baluns and UnunsBalun
OCF dipoleYagiWindomG5RV
UnunVerticalLong wireLoop
Uses for Baluns and Ununs
Uses for Baluns and Ununs
The ProjectHF antenna capable of multi-band operationOff-Center-Fed (OCF) dipole looked good –
tuner not requiredOCF presents 200 Ω impedanceNeeded a 4:1 current balun to transform
200Ω to 50 ΩArticles by Jerry Sevick, W2FMI (SK)Amidon Associates
The Project
W2FMI 4:1 –HBM200 BalunFT-240-K ferrite coretwo 14 AWG bifilar
windings, 100-ohms each
15-mil teflon sleeve1MHz – 50MHz
range2KW continuous4KW peak98% 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
2/31/3
coax
4:1 balun
1:1 lineisolator
Yaesu897D
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
1994Amidon Associates, http://www.amidoncorp.comPalomar Engineering, http://www.palomar-engineers.com
Questions?