T9B: Parasitic beam directional antennas; polarization, impedance matching and SWR, feed lines, balanced vs. unbalanced (including baluns)


A directional antenna is an antenna that sends and receives radio energy mainly in one direction.

A Yagi antenna is constructed using two or more straight, parallel elements that are fixed in line with each other.

Most parasitic beam antennas have one directly driven element.

A parasitic beam antenna is an antenna in which some elements obtain their radio energy by induction or radiation from a driven element.

The directors or reflectors of a Yagi antenna are parasitic elements.


A cubical quad antenna is constructed from two or more parallel four-sided wire loops, each approximately one-electrical wavelength long.
A type of non-directional antenna that is easy to make at home and works well outdoors is a ground plane.

The electromagnetic-wave polarization of most man-made electrical noise in the HF and VHF spectrum is vertical.


The term standing-wave ratio is the measurement of the ratio of the maximum to minimum voltages on a feed line.
You install a balun to feed a dipole antenna with 50-ohm coaxial cable between the coaxial cable and the antenna.

Coaxial cable makes a good antenna feed line because it is weatherproof, and it can be used near metal objects.