1. Baluns, Chokes and UNUNs
Presented by
Andy AE8J

2. What we will cover Common mode chokes Baluns Ununs Why we need them
Feed line currents
Differential mode current
Common mode current
Measuring common mode current
How common mode chokes work
Types of common mode chokes
Air core chokes
Bead chokes
Toroid chokes
Baluns
Current baluns
Voltage baluns
Impedance ratios
How to test a balun
Ununs

3. Baluns, Chokes and UNUNs
What are they ?
Will they lower my SWR ?
Survey the group here.
Who uses baluns or chokes ?
Why did you decide to use them ?
Will they increase antenna bandwidth ?
Why do we need them ?

4. The unfortunate truth
“No other area of technology is so vastly misunderstood as Baluns (and RF Chokes). The web is full of all kinds of misleading and/or wrong information on this topic. At least 50% written in the Internet about baluns is false.”
Rick Westerman, DJ0IP / NJ0IP
“Don’t believe anyone who claims to be an expert on baluns.”
Bernie Huth, W4BGH
“Baluns can be difficult components to analyze and understand fully.”
Steve Hunt, G3TXQ
“Very few people fully understand this technology and as a result it is still far from reaching its full potential.”
Jerry Sevick, W2FMI
Most confusing and misunderstood devices in ham radio.
A lot of confusing, conflicting and flat out wrong information on the internet.
Many grey areas and blurred lines

5. Why do we need them ? Antenna system balance
Many ham radio antennas are balanced
λ/2 Dipoles, Yagis, Loops, Quads, etc.
Twin lead, Ladder line, Window line
Coax is unbalanced transmission line
Antenna may not be symmetrical
Feed line is not perpendicular to the axis of the antenna
Proximity of surrounding objects, ground conditions
Feed point impedance of many types of antennas does not match 50 ohm coax
Folded Dipoles, OCF Dipoles, Windom, End feds, etc.
COMMON MODE CURRENT in a feed line is caused by an unbalanced antenna system
Radiation pattern distortion
Feed line radiation, RFI
Noise pickup on receive
Coaxial cable is not symmetrical.
One side of coax is grounded at the transmitter.

6. Transmission line currents
There are two methods or “modes” by which RF current flows in an antenna feed line
Differential mode current (good)
Occur when antenna is balanced and feed line is balanced
Feed line current is equal in amplitude and opposite in polarity
Maximum transfer of energy from feed line to antenna on transmit
Maximum transfer of energy from antenna to feed line on receive
Common mode current (bad)
Occur when the antenna and/or feed line is not balanced
Radiation pattern distortion
Feed line radiation, RFI, RF in shack, RF burns & shocks
Becomes more of a problem at higher power levels
Noise pickup on receive

7. Differential Mode Currents (good current flow)
Balanced antenna fed with balanced transmission line
Half wave dipole fed with ladder line.
Measure RF voltage from each side to ground.
AC current demonstration here
Differential mode currents I1 and I2 are equal in amplitude and opposite in polarity. The resulting electromagnetic fields in the feed line, because of their close proximity, cancel each other out. No radiation from the feed line.
No low impedance path to ground

8. Common Mode Current (bad current flow)
Balanced antenna fed with unbalanced transmission line
Because of “skin effect” coax becomes 3 conductor.
Instead of a dipole antenna you have a tripole antenna.
For a dipole feed line is vertically polarized
Explains why trimming the coax changes the SWR
Differential currents I1 and I2 cancel each other inside the braid. Because of “skin effect” outside of braid becomes a third conductor. There is no opposing current to cancel I3.
Provides a low impedance path to ground

9. Radiation Pattern Distortion
Hard to measure radiation pattern distortion.
Affects gain and directivity
λ/2 Dipole with common mode distortion λ/2 Dipole no common mode distortion

10. Measuring common mode currents
RF current meter MFJ-854
Differential mode currents in coaxial feed line are equal and opposite so they cancel each other out
RF current meter only measures common mode currents flowing on the outside of coax braid
Show home brew current meter

11. Common Mode Chokes Air core chokes (Ugly Baluns) Coaxial Choke
Can be effective for single band antennas
Air core choke impedance is all reactive and frequency dependent
Not the best choice for multi-band antennas

12. How common mode chokes work
Current flowing through a wire develops a magnetic field around it. Magnetic lines of
force are referred to as FLUX
Coiling the wire concentrates the magnetic field increasing the FLUX DENSITY
Flux density can be further intensified by placing a magnetic material inside the coil
Flux density presents a high impedance (Z) to common mode currents

13. Magnetic Core Material
Ferris materials respond strongly to a magnetic field. Iron oxide, Nickel, Zink, Manganese and Cobalt are combined with ceramic to form a variety of magnetic materials or “ferrite mixes” with varying properties. The ability of a material to intensify a magnetic field is referred to as PERMEABILITY (µ). The higher the permeability the greater the inductance.

14. Ferrite Compositions

15. (Not to be confused with a ferret choking)
Ferrite Chokes
(Not to be confused with a ferret choking)
Super choker
Use bead choke on hex beam
Ferret Choke
Ferrite Choke
W2DU Bead Choke

16. Toroid Choke (Balun) Balanced output Unbalanced input
Highest inductance configuration.
Here the choke coil is formed with 50 ohm coax.
There is no impedance transformation so the choke(balun) is 1:1

17. Explain different core types

18. Definition
Many companies often call the same item different names to confuse you or make it difficult to compare the same item between companies.  So let’s set the record straight and avoid the confusion with product names.  A feed line choke is also called a common mode choke, a 1:1 balun, a 1:1 unun, a current balun/unun, a line isolator, a feed line current choke, and a 1:1 Guanilla balun/unun/choke.  All these names are for the same item: a common mode current suppression device that work to suppress common mode current on the outside braid of your antenna feed line.

19. Baluns
A Balun is a type of broad band RF transmission line transformer that can perform three basic functions:
Unbalanced to balanced conversion of current or voltage
Rejection of common mode currents with some configurations
Impedance transformation with some configurations (impedance ratios other than 1:1)
The word balun is a contraction of the term
“balanced to unbalanced”
Common mode rejection and no impedance transformation (1:1 current balun)
Impedance transformation and no common mode rejection (4:1 voltage balun)
Common mode rejection and impedance transformation (4:1 current balun)

20. Balun Impedance Ratios
1 to 1 BALUNs are used mostly with center-fed dipoles. (aka Chokes) 1.56 to 1 BALUNs are used for vertical antennas or antennas using a counterpoise (aka UNUN) 2 to 1 BALUNs are employed with high-frequency Quads and loop antennas (above 40 meters). 4 to 1 BALUNs are commonly used with Windom's, Off-Center fed dipoles, and Sky-wire loops cut for 75/80 and 160 meters. 6 to 1 BALUNs are sometimes used with antennas that are fed with 300 ohm feed line. 9 to 1 BALUNs are the BALUN of choice when feeding end-fed, long-wire antennas fed with 450 ohm feed line.
Uses for some standard impedence ratios

21. Types of Baluns Two basic types of baluns Current baluns (Guanella)
Places an inductance in series with the balanced terminals
Forces equal currents at balanced terminals
Impedance matching 1:1, 4:1, 6:1, 9:1, etc.
Prevents common mode currents
Lower insertion losses
Preferred for most amateur applications (current fed)
Voltage baluns (Ruthroff)
Places an inductance across the balanced terminals
Forces equal voltages at balanced terminals
Does not prevent common mode currents
Higher insertion losses
Mainly used in long wire and end fed type antennas (voltage fed)
Voltage baluns are also used for antennas where we want feed line radiation
Carolina windom and G5RV. Also used at the output of some antenna tuners.

22. Current Baluns (Guanella)
Wire can be either coax or bifilar wound.
Explain crossover winding
1:1 current balun is the basic building block

23. 4 : 1 Current Balun (Dual Core)
Unbalanced input
Balanced output
Point out input and output connections
Point out specs
This is the preferred 4:1 current balun

24. Voltage Baluns (Ruthroff)
Voltage baluns are autotransformers not flux coupled transformers
Explain bifilar and trifilar windings and convention dots
Explain impedance transformation square of turns ratio

25. 4 : 1 Voltage Balun

26. Transmission Line Baluns

27. Testing a Balun What type of balun ?
Testing a balun with an MFJ-259B antenna analyzer
LDG RBA-4:1 Voltage Balun
Terminate balanced input with 200 Ω resistor
Sweep analyzer thru frequency range
Analyzer should read 50 ohms and low
SWR throughout frequency range
What type of balun ?
Testing a current balun
Testing a voltage balun
Demonstrate how to test a balun

28. Quotes from the experts
“Current baluns, rather than voltage baluns, should be used whenever possible. Current baluns provide better balance and often have lower loss. Current baluns, especially 1:1 ratio baluns, tolerate load impedance and balance variations much better than voltage baluns.”
“Most commercially produced baluns are Voltage- type baluns. The "Current-type balun™" is superior to simple 'Voltage-type' baluns in several ways. The most important are better output balance and higher feedline-to-antenna isolation. This means you enjoy improved antenna radiation patterns and less problems with TVI, RFI and RF feedback.”

29. When is a Balun not a Balun?
When it’s a UNUN
4:1 Unun
4:1 Balun
Note common ground connection

30. Ununs Unbalanced to Unbalanced transformers
Both input and output are unbalanced
Does not provide common mode current suppression
Used to feed unbalanced antennas with coax
verticals, inverted L’s, long wires, etc.
Available in 2:1, 4:1, 6:1 and 9:1 impedance ratios
Note common ground connection
Impedance ratio=turns ratio²

31. UNUN Specification
Unbalanced input
Unbalanced output

32. UNUN for vertical antennas
32 ohm to 50 ohm impedance matching
Unbalanced input
Unbalanced output

33. Thanks for your attention