AM Radio ProjectSean Ryan, Jamie Shaw and Paul Olney

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.

AM Radio ProjectA 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.

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.

The ScienceA 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.

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.

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.

ConclusionAn 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.