The sources and properties of radio
Making radio waves - transmitter: Radio
waves, like all EM radiations are oscillating electric and
magnetic fields, and are produced by alternating electric
Alternating currents automatically produce an oscillating
electric and magnetic field that makes the electric
charges (electrons) oscillate and this automatically
produces radio waves if the oscillations of that frequency.
The frequencies of the waves produced
will equal the frequencies of the alternating current - however complex
the signal transmitted.
The diagram below illustrates the
principles of how radio signals are generated, transmitted and received.
The oscillating charges produces and emit an EM wave
of radiation - radio waves. The EM wave has the same frequency
as the a.c. current that produced it - so a radio transmitter circuit uses
a.c. frequencies in the EM radiation band to create
radio waves of the desired frequencies.
Receiving radio waves: EM waves can cause charged
particles like electrons to oscillate at the same frequency. If these
electrons are part of a 'receiver' electrical circuit, an alternating current is
induced at the same frequency as the EM wave - this is what a radio receiver
aerial (antenna) does and the rest of the electronics produces the
sound and pictures.
You can demonstrate by feeding a
signal from a microphone or signal generator into an oscilloscope and
into a radio transmitter circuit.
The signal from the radio
receiver can then be fed into a 2nd oscilloscope.
You can then compare the
generated signal with the received signal and they should be the
same, however complex the signal may be.
In real radio
frequencies use a carrier
a pure wave of
constant frequency, a bit like a sine wave
and has imposed on it the more complex wave of the signal
The process of imposing an input signal onto a carrier
The above descriptions about radio waves apply to microwaves too,
The combination of transmitter
(e.g. radio mast) and receiver (e.g aerial) allows you to
encode information onto a radio signal and transmit information from one
place to another - its essentially a data transfer system which might be
a radio signal or TV .
Radio waves do penetrate liquids and
solids but are gradually absorbed and end up as heat energy - increasing the
thermal energy store of the surroundings.
Radio waves pass straight through the
human body without causing harm.
Uses of radio waves
Radio waves are EM radiation with
wavelengths greater than 0.1 m.
Long-wave radio waves can be transmitted
over long distances, in fact all the way around the Earth. They have long
wavelengths of 1-10 km and can diffract around the surface of the Earth and
around hills too and reflect/refract off the ionosphere - see diagram and
This means radio signals can be
received even if the transmitter and receiver are not in direct line of
Reflection/refraction of radio waves
Short-wave radio signals of wavelength
~10 m to ~104 m can also be transmitted and received over long distances
because they are reflected off the ionosphere (which is an electrically
charged layer of the Earth's upper atmosphere).
The lower atmosphere is not
electrically charged and does not inhibit the transmission of radio
waves or microwaves.
However, part of the upper
atmosphere, called the ionosphere, contains electrically charged
particles (ions) that interfere with radio waves e.g. reflect them,
and so they zig-zag through the lower atmosphere travelling over
thousands of km from transmitter to receiver.
Radio waves are used to transmit
information from one
location to another e.g. to your TV and radio 'appliances' for
you to view and/or listen to.
TV and FM radio use very short radio
waves and other radio transmissions use medium and longer wavelengths (MW
and LW). To get a good reception, you do need to be in direct sight of the
transmitter because these waves do not diffract (bend) around obstacles and
they don't travel through buildings.
Bluetooth devices use low
power short wavelength radio waves to
communicate and send data between devices like mobile phones or computers relatively close together - so the
radio waves only have to travel short distances. The distances between
devices are quite short i.e. within a few metres of each other.
This avoids the use of wires e.g. the
wireless headset you use to use your phone while driving a car.
diffraction of radio waves
You can pick up a long
wavelength (lower frequency long wave) radio signal with your radio receiver
without being in a direct line with the radio transmitter because these
radio waves are diffracted by hills and other large obstacles.
The wavelengths of 'long wave' radio
waves can be over a km, which is similar to the width of hills.
You can also pick up long wave
radio signals over large distances because they can diffract around the
For a good reception of higher
frequency (shorter wavelength, 'short wave') TV and FM radio signals, you
need to be in direct line with the transmitter, unlike 'long wave radio',
the signal shows little diffraction ('bending').
Short wavelength, high frequency
radio signals, can also be received over large distances because these
signals can bounce of the Earth's surface AND the ionosphere - an
electrically charged layer of the Earth's upper atmosphere - the waves
effectively zig-zag between the Earth's surface and the ionosphere (==
Unlike microwaves, radio waves are
refracted by some layers of the atmosphere, so cannot be used for satellite
You can now use high-frequency radio wave
scanners to security checks on passengers and luggage at airports.
Radio waves are much safer than using X-rays.
Dangers of radio waves?
I don't know of any? Does political
propaganda count?!!! (just a joke!)
Radio waves are of long wavelength
and low frequencies and so carry little energy and pass through our body
without doing any harm - as far as I know?