P66

DTMF Control Tones

DTMF Audio Tone Control on Repeaters

Foundation Licence candidates are required to demonstrate the correct use of voice repeaters.   Part of that is the need for a basic knowledge in audio tones that are used to access and control.  This includes the use of Dual Tone Multiple Frequency (DTMF) access control systems.

This abbreviation stands for Dual Tone Multi Frequency.  These are brief control tones that are sent when a button is pressed.  Often this will be buttons on the back of the radio microphone.  They are needed for Internet Linked repeaters, Echo link and sometimes for local repeater functions such as automatic signal reports.

When one button is pressed two tones are generated in a form of matrix.  Each is deliberately non-harmonically related.

In this example, button 9 is pressed on a microphone and the tones 852 Hz and 1477 Hz are briefly transmitted (For as long as your finger is on the button).  To determine what each button actually does, you need to consult details of the service you are attempting to use.

This video clip describes how these tones are used:

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 on using DTMF can be found from Chapter 3, Page 67 in this book

ACMA Syllabus Extract

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

8.5  Operating through a Repeater

Recall and demonstrate, using supplied reference material, the correct use of voice repeaters, including the use of continuous tone-coded squelch system (CTCSS) and dual tone multiple frequency (DTMF) access control systems.