P43

Using a Dummy Load

When testing a transmitter, it is good practice and common courtesy to use a dummy load to prevent your test signals from being radiated and annoying or causing interference to other users on the bands.

A dummy load is a useful piece of test equipment that mimics an antenna, except that it dissipates the applied RF energy from a transmitter as heat, instead of radio waves. It’s usually a large 50 Ohm Carbon-film resistor that’s fixed into some kind of heat sink housing. Alternatively, a variety of smaller resistors in different series/parallel combinations that sum to 50 Ohms may be housed in a ventilated container.

Larger dummy loads are often immersed in oil, enabling them to dissipate higher power levels

Dummy loads may also be used as a method of testing coax cable integrity

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 Dummy Load usage and transmitter testing relevant to Foundation Level Qualifications  can be found in this book from Chapter 5, on Pages 46 & 47

ACMA Syllabus Extract

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

5:16 Testing Transmitters

Recall that when testing a transmitter, a non-radiating load (dummy load) is commonly used to prevent a signal from being radiated