P44

Identifying Common Antennas

The Five Basic Antenna Types

There are five basic antenna types that all Amateur operators must be able to recognise.   These are summarised in the image below.  Each has unique characteristics which make them more or less appropriate for different situations.

Be aware that the size / length of the antenna is inversely-proportional to the frequency, which is to say as the frequency in use increases, the matched antenna will be smaller / shorter.

For example, Antennas for HF long range communications will often be made from long lengths of wires tied between trees, whereas VHF and UHF are much smaller antennas made from sections of aluminium tube.

Polarisation and Directionality

Two key aspects that affect the performance of all antennas is the direction in which antenna may radiate (or receive) and the orientation or ‘polarisation’ of the antenna.

An antenna which is physically oriented vertically will transmit a vertically oriented signal.  This is called Polarisation.  A transmitted signal must be received on an antenna with the same polarisation, or the received signal strength will be significantly diminished.  Generally antennas will be either Horizontal or Vertical. (Be aware there are some specialised designs which use ‘circular’ polarisation.)

Antennas which radiate in all directions on a horizontal plane (such as a vertical antenna on a vehicle) are called Ominidirectional Antennas.  

Antennas which radiate equally to the front and rear of an antenna (such as a dipole antenna) are called Bi-directional Antennas

Antennas which radiate in a single dominant direction, (such as a Beam Antenna) are called Unidirectional Antennas.

Below is a video which describes the different antenna types in greater detail.

The Foundation Level Study Guide

All Blue Tiles form part of the syllabus for the Foundation Level Recognition Certificate (operator licence).  A primary source of information for many of the blue tile topics can be found within the Foundation Level Study Guide.  This is a free download available at:

https://vkradioamateurs.org/flsg/  This is a digital book and contains many links to other resources and explanatory videos.

Information about Amateur Antenna Types can be found in this book from Chapter5, on Pages 32 through to 37

ACMA Syllabus Extract

According to the ACMA Foundation Syllabus, the required knowledge on this topic is:

5.4 Antenna Purpose

Recall that the purpose of an antenna is to convert electrical signals into radio waves, and vice versa

5.5 Antenna Length to Frequency Relationship

Recall the relationship between the physical length of the antenna and the frequency of operation.

5.6 Identification of Common Antennas

Recall the Amateur Class Licence authorises operation on certain frequency bands. Recall in which document the bands are specified.

5.7 Choice of Antenna

Recall that the on-air performance of an amateur station can be improved significantly by the correct choice of antenna.

Identify, using supplied reference material, the symbol for an antenna.

5.8 Antenna Directional Characteristics

Recall the meaning of the terms: polarization, omni-directional, bi-directional, unidirectional and gain as they apply to antennas.

5.9 Polarisation

Recall that the polarisation and directivity of an antenna is determined by its physical construction and orientation.