2. Introduction
The aim of this investigation was to construct
and test an AM radio, as well as to research,
demonstrate and explain how an AM signal is
transmitted and received.
3. AM Radio Project
A simple AM radio was constructed over a
period of weeks from the relevant components
consisting of a tuning circuit, a demodulation
circuit and an amplification circuit.
The radio was then tested and results were
recorded and evaluated.
4. Results?
Only two radio stations were able to be
received, BBC Asian Network, and Sabras
radio.
These were able to be picked up because the
transmission towers for these radio stations
are very close by.
5. The Science
A signal is received within an antenna by causing the free elections (the
particles that conduct a current through a circuit) to oscillate at the same
frequency within the antenna back and forth and thus inducing a small
current within the radio circuit.
As the audible sounds are placed within an inaudible carrier wave, this
audible tone must be demodulated from the carrier. Using ‘Envelope
detection’ from which the audible sound is deduced from the higher
frequency ‘envelope’ using a specialised diode, the remaining higher
frequencies can then be removed using a capacitor leaving the original
audio signal.
This demodulated signal then has to be amplified so it can be heard
through a loudspeaker which is achieved using a transistor that uses
three pins: a base, a collector and an emitter. When the small current
passes through the base to the emitter, the transistor becomes a
conductor which allows a much larger current to pass from the collector
to the emitter, thus amplifying the signal.
6. AM transmission
Demonstration
A demonstration of an AM transmission was
carried out in the lab using an Oscilloscope
and a function generator.
Our own signal was generated then picked up
by the receiver and the signals were shown on
the Oscilloscope to show a visual of how an
AM transmission works.
7. Results?
AM transmission works by sending a high
frequency carrier signal that is modulated by
varying the amplitude of the signal.
This modulation creates an ‘envelope’ in which
an audio signal can be stored.
This is then transmitted where the receiver
picks up the signal, demodulates it to
separate the audible signal from the
carrier signal, and then amplifies it.
8. Conclusion
An AM signal is transmitted by the way of a
high frequency carrier signal that is modulated
to hold an audible wave.
This signal is received and demodulated by
the radio, to separate the audible signal from
the carrier.
It is then amplified so it can be heard through
a loudspeaker or a pair of headphones.
