Understanding where you are on the radio spectrum, whether you are transmitting or listening, can be complicated. But it can be a whole lot easier if you understand the key terms and what they mean.
Frequency
Radio waves use electro-magnetic energy and are measured in: –
- Hertz (or Hz);
- Kilohertz (KHz);
- Megahertz (MHz); and
- Gigahertz (GHz).
So, for example, PMR446 Channel 3 is on 446.03125MHz. Anyone familiar with PMR446 will know where Channel 3 is. But if they are not familiar with it, then telling them that you are on 446.03125MHz will enable them to pin-point your exact location.
Most hobby radio uses frequencies between 1.8Mhz and 1296Mhz, although radio amateurs have the use of some higher and lower frequencies too.
You’ll also hear people referring to : –
High Frequency or “HF” – this 3 to 30MHz
Very High Frequency or “VHF” – 30 to 300MHz
Ultra High Frequency or “UHF”- 300 to 3000Mhz
Super High Frequency or “SHF” – 3000 to 30000MHz (3 to 30GHz)
Wavelength
Radio waves can also be measured by their length in metres (this is the length of the radio wave). They can be extremely small (millimetres) or very long (thousands of metres) and anywhere in between.
As the frequency of radio waves increases, their length decreases. The higher the frequency, the smaller the wavelength.
For example, the waves at 27MHz (CB Radio) are about 11m long. At 446Mhz (PMR) the waves are much shorter at about 67cm.
You will hear people referring to “11m”, for example.
Bands
A specific point on the radio spectrum is referred to by frequency. The frequencies between two points on the spectrum are referred as ‘bands’ usually by wavelength but sometimes by name.
So, the range of frequencies between about 26MHz and 28MHz (used for CB radio) are known as the “11m band”, because the wavelength at these frequencies is roughly 11m. But the PMR446 band is known by its name (“PMR446”) – we don’t call it “67cm”, even though that is the wavelength at 446Mhz.
The word ‘band’ is also used to divide the radio spectrum up into subsections.
Within the 11m band, there are several sub-sections referred to as “Low Band’, “Mid band” and “High Band” and in the UK, the original allocation, known as the “UK FM band”. Knowing these sub bands can be useful if, for example, someone says “I’m on mid-band CB, Channel 19”. If you hear this, selecting Channel 19 on a UKFM CB Radio won’t get you there because these radios only have the UKFM sub-band.
Sometimes, manufacturers divide up the frequencies available on their radios which they label something like “Band A”, “Band B” and so on. These are usually only relevant to those radios. So, it is not usually very useful to say “I am on Band A”, for example, as it won’t mean anything to anyone who doesn’t have a radio with the same sub-band divisions.
Channels
Some bands are also divided into groups of ‘channels’. These are particular frequencies arranged with equal gaps between them. The PMR and CB bands and sub-bands are arranged in this way. There are also channels on some amateur bands, mainly where the FM mode is used, but nowadays these tend to be referred to by their frequency rather than their channel ID.
Sometimes, people refer to the memory number on their handheld or other radios as “channels”. But this will only be meaningful if people have exactly the same memories set up as yours (which is unlikely), so referring to them in general use is not a good idea.
If all else fails, always refer to the FREQUENCY (if you know it), as this will indicate your exact location on the radio spectrum!