Feeding the Antenna

Once we have an antenna, we need to connect it to a transmitter in such a way that delivers as much of the transmitter power as possible to the antenna (or so that the antenna delivers power to the receiver). While there are cases when the antenna can be connected directly to a transmitter, most often we use some sort of feedline to connect from one to the other, especially when the antenna is high in the air, or otherwise at a distance from the rig. In addition to connecting the two, for maximum efficiency we need to match the impedance of the antenna to that of the feedline, and the combination of the two to the transmitter.

Transmission Line Theory

First, let’s consider some basic Properties of Transmission Lines.

Understanding Antenna Impedance.

SWR (Standing Wave Ratio): what it means, and what it doesn’t.

The Smith Chart, a graphical calculator of impedance along a transmission line.

Coaxial Cable (“coax”): types and properties.

Parallel Conductor Lines, including ladder line, twinlead, open wire line, “zip cord”, speaker cable, etc.

Feedline Losses can have a big impact on your station efficiency.

Impedance Matching – an overview

The role of the Antenna Tuner, also known as an ATU, Matchbox, Transmatch, etc.

Baluns: dealing with “balanced” and “unbalanced” lines and loads.

Impedance matching using Transmission Lines

Impedance matching using Other Feed Methods

Transmission Line Projects

Simple SWR indicators

Making your own transmission lines.

Small 1 : 1 balun for portable antennas

Using 75 ohm coax with a 50 ohm transmitter

Antenna Tuner Projects

Simple L-network tuner for HF.

Balanced tuner for portable use

Analysis of the Unique Wire Tuner

Adjusting your antenna tuner for maximum efficiency

Baluns for use with antenna tuners.

Dual-band matching network

Open wire stub tuner

W1ICP’s “Ultimate Transmatch