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Amateur radio bands

This activity introduces the concept of amateur radio bands and provides practice in their use.

Introduction

All radio communication uses radio waves. It is radio waves which carry my voice from my transmitter to your receiver. They are so incredible that they can sometimes carry my voice all around the world. They can bend around mountains, fly high into the sky, come back down and bounce off the earth again like a football - all at the speed of light. Even faster than Superman! Radio waves are not all the same, though. They each have different frequencies, which is good because now we can tell them apart. We can use radio waves on different radio frequencies to talk to different people at exactly the same time.   

Radio frequency spectrum

The radio frequency spectrum is like a telephone book of all the radio waves that we know of. You can look them up by their number (that is their radio frequency). But radio frequencies are a precious resource. They can't be used by different people at the same time for different purposes. For example, if I am using a radio frequency to talk to my friend, you have to use a different frequency to talk to yours. So the radio frequency spectrum is allocated to different groups of people, for different important uses like: Broadcasting, Satellites, Aeroplanes, Boats, Vehicles, Science and Astronomy etc. 

Segments and bands

There are so many radio frequencies in fact that the radio frequency spectrum has to be divided into eight different segments for our convenience. Radio waves are divided into the following segments: Very Low Frequencies, Low Frequencies, Medium Frequencies, High Frequencies, Very High Frequencies, Ultra High Frequencies, Super High Frequencies and, wait for it, Extremely High Frequencies. Radio waves in each segment has their own characteristics of sorts: VLF waves can travel under water, HF waves can bounce around the planet. EHF waves couldn't even make it through a wet phone book, but they are just fine going to the moon and back. The good thing is that amateur radio operators, who spend a great deal of their time learning about all these radio wave characteristics, have been allocated their own frequency bands for just that purpose. There is at least one amateur radio frequency band in almost every segment of the radio frequency spectrum.

Primary and secondary services

But as I said the radio frequencies are a precious resource, so sometimes we have to share them with others. That means that two different groups can use the same frequency band provide that the secondary service (that is usually us by the way) don't cause any interference to the primary service (e.g. Commercial broadcasters). Anyway, we always listen on the frequency we intend to use to see if anyone is using it and find another one if they are.

Modes

Of course we have to share the amateur radio bands with our fellow amateur radio operators. So we also have to allocate different parts of our bands to the different modes which we like to use. Those modes could be Voice, or Morse code or Digital modes etc. There are quite a few as we shall see.  

ACMA spectrum chart

Amateur radio band plan

Here is an example of one amateur radio band plan. It is for the 40 metre amateur band, which is available to all classes of amateur radio licences. It covers 7000kHz to 7300kHz. Amateurs are the Primary Service in the bottom 100kHz of the band and the Secondary Service in the top 200kHz of the band. Different parts of the band are allocated to CW (Morse code), SSB (Voice) and digital modes of operation.

 40 metre band plan showing CW, SSB and Digi segments

Preparation

  • You will need a large A3 print out of the radiofrequency spectrum

Activity

  • Ask the students to work out how many amateur radio band there are.
  • Ask the students questions like:
    • "On what frequencies can I transmit Voice on the 40 metre band as a primary service?"
    • "What is the main VHF frequency band used for aeroplanes?"

Homework