# UK Amateur Radio ## Foundation Licence 2002
### Technical Basics Part D
### Frequencies used in power, audio and radio systems.
Two abbreviations that you must know are
RF = Radio Frequency | AF= Audio Frequency
### FREQUENCY & WAVELENGTH You have learned that we measure frequency in Hertz and that the frequency of the AC electrical supply in your house is 50Hz. Before talking a bit more about other frequencies you must understand the idea of a 'cycle' a bit better. The most important type of changing signal we see is a 'sine wave' which looks like this:-
The above diagram shows one complete cycle between A & B - making the diagram show more cycles of the same signal would just be a 'repeat', joining another drawing with the A to the B as many times as required. The distance covered before the signal repeats - that is the distance between A & B is known as the WAVELENGTH for which we use the symbol . In fact as long as the points A and B are in the same relative positions it would still measure the wavelength. We measure wavelength in metres or m. There is a formula to convert frequency and wavelength but the good news is that you don't need to learn it for the Foundation Licence but you do have to understand how to use a simple chart that will do the conversion for you. This is covered in the next section.
### Sine Wave generation Have you ever thrown a stone into a puddle? Of course you have. What happened? Well if it was a big stone there would be a great big splash - which is not really what I was thinking about. What about if you drop a small stone into the puddle? There would be ripples or "waves" going away from where the stone went into the puddle. After awhile the ripple fade away because it was only one stone. What it you put your hand in the puddle then take it out then out it back in again. Ripples occur each time. In fact your hand oscillates between being in the water and out of it. To OSCILLATE means to do the same thing over and over again. Thus it is said that the waves are created by an Oscillator and thus in a radio there are one or more frequency oscillators. You can also make "wave" in your bath to experiment so you don't have to wait for a rainy day to try it out !!!!
### Different signals have different frequencies
These are the frequencies that you must know you are not given a chart for these in the written assessment
50Hz | Mains supply
100Hz to 15,000Hz | Normal hearing of the human ear
300Hz to 3kHz | Range for commercial audio communication
1.8MHz to 30MHz | HF amateur band
30MHz to 300MHz | VHF band
145MHz to 146MHz | VHF amateur band
300MHz to over 1000MHz | UHF band
430MHz to 440MHz | UHF amateur band
kHz =1,000Hz MHz = 1,000,000Hz
### Radio Spectrum The radio spectrum as it is called is divided into the bands so that frequencies can be allocated to various use. You must be familiar with (but you don't have to learn it) the following table (which will be available to you in the written assessment) :-
You will be given this chart in the written assessment
Frequency | Use
87.5 to 108.0MHz | Broadcasting
108.0 to 117.975MHz | Aeronautical Radionavigation
117.975 to 137.0 MHz | Aeronautical Mobile
138.0 to 144.0MHz | Land Mobile
144.0 to 146.0MHz | Amateur & Amateur Satellite
146.0 to 149.9MHz | Mobile except aeronautical mobile
149.9 to 150.05MHz | Radionavigation-Satellite
150.05 to 152.0MHz | Radio Astronomy
152.0 to 156.0MHz | Land Mobile
156.0 to 158.525MHz | Maritime Mobile
158.525 to 160.6MHz | Land Mobiles
160.6 to 160.975MHz | Maritime Mobiles
So what is the important point to learn from the above table that :- YOU ARE NOT ALONE in the radio spectrum In fact the Amateur Radio bands are sandwiched tightly between other services so we must ensure that our signals to not go outside the "Band Edges" and cause interference to others.

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