Feeders

• Half wave dipoles, yagis and loops are balanced antenna, i.e., voltage and current are balanced each side of the centre feed point;  coaxial cable is an unbalanced line
• A Balance to Unbalance matching device called a BALUN is used at feed point.  If not, radiation can occur from coax outer, reducing efficiency
• The antenna’s radiation pattern changes if the currents in the driven element of a balanced antenna are not equal and opposite
• A Balun can also be designed to provide impedance transformation (transformer balun)
• Alternatively a balanced line and ATU could be used

Course Guide Topics

1. Purpose
2. Types of feeder
3. Characteristic Impedance
4. Parallel Conductor Line
5. Preventing Line Radiation
6. Balanced Line
7. Coaxial Line (Coax) (1)
8. Coaxial Line (Coax) (2)
9. Waveguide
10. Velocity Factor
11. Velocity Factor (Contd)
12. Terminated Line
    (Matched Case) (1)
13. Terminated Line
    (Matched Case) (2)
14. Terminated Line
    (Unmatched Case)
15. Standing Waves (1)
16. Standing Waves (2)
17. Standing Waves (3)
18. Line Loss (1)
19. Line Loss (2)
20. Matching
21. Matching – Quarter Wave Transformer (1)
22. Matching – Quarter Wave Transformer (2)
23. Lines as Tuned Circuits
24. Open Circuit
25. Short Circuit
26. Stubs
27. Stub Characteristics
28. Antenna Tuning Units – ATU
29. Balance/Unbalance
30. Baluns
31. Typical Baluns
32. 1:1 Current Balun
33. 4:1 Voltage Balun
34. 1:1 Voltage Balun
35. 4:1 Transmission Line Voltage Balun