1. Baluns, Ununs and Isolators
What You Need To Know
Hap Griffin WZ4O

2. The Standard Half-Wave Dipole
Presents a balanced load to the transmission line

3. Balanced vs Unbalanced Transmission Lines
In a balanced line, the balanced and 180 degree out of phase currents exactly cancel at any point in space outside of the line (no radiation).
In a coaxial line, the fields are contained inside the shield and do not radiate to any point in space outside of the line (no radiation).

5. How a Dipole is Designed to be Fed

6. Dipole Fed Directly by Coaxial Cable

9. What is a Balun?
A Balun is a special type of RF transformer (consisting of transmission line elements) that perform two functions:
Primarily – Balanced to Un-balanced transition (or Vice-Versa) to reduce or eliminate Common Mode current on the shield of unbalanced transmission line (coax)
Secondarily – Can be used to transform impedance
The word BALUN is a contraction of “BALanced to UN-balanced transformer)

10. Why Might Impedance Transformation Be Required?

13. A Voltage Balun attempts to provide equal and opposite VOLTAGES at the two output terminals.
A Current Balun attempts to drive equal and opposite CURRENTS into the two output terminals.

14. Typical Voltage Balun – W2AU
Note the Bifilar or Trifilar windings – these are actually short transmission line elements
The transmission line elements are physically short compared to the wavelength of operation, so are broadbanded and operate over a wide frequency range.

15. Voltage Balun with Impedance Transformation
4:1 “Ruthroff” Voltage Balun

16. 1:1 Ruthroff Voltage Balun

17. 1:1 Ruthroff Voltage Balun

18. 4:1 Ruthroff Voltage Balun

19. 4:1 Ruthroff Voltage Balun

20. Voltage Baluns Using ¼ Wavelength Sections of Transmission Line - Narrowband

21. Current Balun, or Guanilla Balun

22. 1:1 Current Balun

23. 1:1 Current Balun

24. 4:1 Current Balun

25. 4:1 Current Balun

26. 4:1 Current Balun

27. Choke Balun, or “Ugly Balun”

28. Choke Balun Made With Ferrite Cores

29. W2DU Choke Isolator “Balun”

34. Conclusions:
If you are NOT worried about pattern accuracy, and DO NOT have RF in the shack problems, you can get away without using a Balun.
Conversely, if you DO care about pattern accuracy, or have issues with RF in the shack, DO use a Balun.
For typical wire antennas, where the legs are likely to have unequal environments, a CURRENT Balun is the best choice.
For yagi’s where the environment is more likely to be symmetrical around the elements, a VOLTAGE Balun is OK.