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?