The Basic lessons · Feedlines and antenna systems · B-006-002

Understanding Feedlines and the Balun

This lesson explains the physical differences between coaxial, window, and open-wire transmission lines. It also clarifies why a balun is essential when connecting unbalanced cables to balanced antennas.

This lesson is part of SignalPrep Pro. The subsection's 11 exam questions are free to practise: practise B-006-002.

What this subsection asks

• What kind of transmission line has a centre wire inside an insulating material that is covered by a metal shield or sleeve?
• What kind of transmission line has two wires side-by-side embedded in insulating material?
• What kind of transmission line is made of two conductors held apart by insulated rods?
• What is the purpose of a balun?
• Where would you install a balun to feed a dipole antenna with 50-ohm coaxial cable?
• What causes a transmission line to be unbalanced?
• What device can be installed to feed a balanced antenna with an unbalanced transmission line?
• What device should you use to connect a coaxial cable to window line?
• A balanced transmission line:
• Your antenna tuner does not have a balanced output and you wish to use window line to feed an HF antenna. What device should you use between the tuner and the transmission line?
• What kind of transmission line has two conductors maintained side by side, a constant distance apart, using insulated spreaders?