UK Amateur Radio
Foundation Licence 2002
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Technical Basics Part D
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Frequencies used in power, audio and radio systems.
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Two abbreviations that you must know are
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RF = Radio Frequency |
AF= Audio Frequency |
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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:-
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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
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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 |
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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 |
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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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