Baluns, Chokes and UNUNs Presented by Andy AE8J

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

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 ?

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

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.

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

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

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

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

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

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

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

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.

Ferrite Compositions

(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

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

Explain different core types

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.

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)

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

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.

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

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

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

4 : 1 Voltage Balun

Transmission Line Baluns

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

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.”

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

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

UNUN Specification Unbalanced input Unbalanced output

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

Thanks for your attention