AM Radio Receiver and Amplifier Experiment

Jessica McCall, Fouzia Chuta and Martin Mills

TECH1002 Studies Into Media Technology

Introduction

During our radio laboratories in weeks 7-15 our task was to build and test an AM radio receiver with an audio amplifier and to be involved in a demonstration of AM transmission. This report will explain firstly the AM radio receiver and amplifier experiment, involving the explanation of the aims and objectives of what the experiment entails. Then the report will go on to discuss the equipment used for this experiment and also the method which was used to construct both parts of the experiment. Finally the report will conclude with the results which were obtained and then an explanation of the results to conclude the experiment. The report will then lead on to discuss the AM transmission demonstration in which the aims, objectives, equipment, method and results will also be explained for this experiment. The report will then conclude with a conclusion which will involve a discussion to how both experiments went. The structure of the report will be as said above allowing both experiments to be explained in detail.

Aims and Objectives – AM Radio Receiver and Audio Amplifier Experiment

The aim of this experiment is to present the making and testing of an AM radio receiver and Audio Amplifier. The reception results will be recorded and explained, and if technical failure presents itself then our experiment will be using sample results (which are typical results used). The equipment will be explained, how it was used and put together including explaining tuning, demodulation and amplification. Also the method of our experiment will be explained which involves the steps taken to make the radio receiver and then describing the method of the audio amplifier. After this the results will then need to be explained which will involve what receptions were gained and not gained.

The objective of this experiment is to try and receive a reception that would either include “BBC Asian Network – 837 kHz” or “Sabras Radio 1260 kHz” using the AM radio receiver that was constructed and hearing the sound from the audio amplifier that was constructed and added to the receiver.

Equipment – AM radio Receiver and Audio Amplifier Experiment

To create our AM radio receiver, we had to use a range of apparatus. The diagram below shows the entire receiver and the equipment used to ensure it functioned.This image shows the three sections of the circuit- tuning, demodulation and amplification, and it also shows the components involved which are as follows:Transistor, variable tuning capacitor, a ferrite rod, around which we coiled the enamelled copper wire to create the aerial, resistors, various other capacitors, a headphone socket and a AA battery holder. As well as creating an AM radio receiver, we also created an audio amplifier. Again, numerous apparatus’ were required in the construction of the amplifier, and the image below is one that a member of our group captured. It shows our own audio amplifier and the components used to create it can be identified, should they need to be.

Figure One

Method – AM Radio Receiver and Audio Amplifier Experiment

This was the procedure which was followed during the construction of the AM radio receiver. It began by taking the ferrite rod and winding the enamelled copper wire around it approximately 55 times. Doing this took two attempts to ensure the coil was correctly wrapped around the rod, and the measurements of the coil fit correctly onto the corresponding parts of the ferrite rod.

It was then necessary to ensure the enamel had been removed from the end of

the wire before soldering the aerial to the circuit board.After this had been completed, the resistors were soldered in place, as were the small capacitors, the BC548B, the MK484 radio IC and the variable tuning capacitor. Once all these components were soldered into place, we could attach the wires to the headphone socket, and then attach the headphone socket to the circuit board itself. After this had been completed, it was then possible to solder the aerial in place, providing that the enamel had been removed from the wire, as mentioned earlier. Finally, the battery holder must be attached to the circuit board.Completing all this should result in a successful, fully functioning AM radio receiver.

To construct the Audio Amplifier, the following procedure is preferably adhered to.To begin with, the resistors must be soldered into place. Once that had been successfully completed, the small capacitors, electrolytic capacitors and the LED can all be soldered into place also. The LED must be surrounded by enough room for movement in the designated case. If this is correct, then the IC socket and any other components may be soldered into place, however the cables must be fed carefully through a hole in the case in order to continue. Now the TBA820M can be placed in the IC socket, and to complete the construction, the battery can be attached and the circuit may now be fully functional.

Figure Two

Figure Three

Results As a group we initially collated the components together and constructed both

parts that were required for the radio, (I.e. the receiver and the amplifier). We correctly soldered the required parts into place on the radio. After constructing these and testing it, we found that the radio was fully functioning. We know this because sound was heard coming out of the speakers of certain radio stations within the frequency it could pick up (One example was the BBC Asian Network which was heard successfully). We also know the project was successful as we were able to tune the sound of the radio up and down to the desirable level

Explanation of ResultsAmplitude modulation produces a signal with power at the carrier frequency which is within the two

sidebands. Each sideband has the same bandwidth to that of the modulating signal, and normally is higher or lower than the carrier frequency. Amplitude modulation that concludes with two sidebands and a carrier is often called double sideband amplitude modulation (DSB-AM). Amplitude modulation is mainly ineffective as when thinking about it in terms of power, a lot is wasted. At least two-thirds of the power is in the carrier signal, which carries no useful information as the remaining power is split between two identical sidebands, even though only one of them is needed since they contain the same information.

When considering demodulation An AM signal encodes the information onto the carrier wave by changing its amplitude in direct line with the analogue signal to be sent. There are two ways used to demodulate AM signals.

The envelope detector is a method of demodulation. It contains of anything that will pass current in one direction only. This could be in the form of a single diode, or something more complex. This was the earliest modulation and demodulation technique used in radio.

 

What the product detector does is that it multiplies the incoming signal via the signal of a local oscillator, which has the same frequency and phase as the carrier of the inward signal. This method will decode both AM and SSB, even if the phase cannot be determined a more complicated setup is required.

An AM signal can be rectified without requiring an approved demodulator. For instance, the signal can be passed through an envelope detector (a diode rectifier). The output will chase the same curve as the input baseband signal. The many forms of AM require coherent demodulation in which the carrier is reduced and suppressed.

AM Transmission Demonstration

Experiment Two

Aims and Objectives – AM Transmission Demonstration Experiment

The aim of the AM transmission demonstration is to generate an AM radio transmission to test this and see if the radio can receive the signal and produce the sound. The equipment which was used to demonstrate the AM transmission will be discussed, and also how and why this type of equipment was used. The report will then lead on to discussing the method of the experiment, why we choose this method which will explain how the demonstration works. Finally the report will explain the results which were gained from the AM transmission demonstration, what was successful and what was not during the AM transmission demonstration. The objective of the AM transmission demonstration is to explain how this type of demonstration works and to test how a higher frequency carrier wave is modulated by a low frequency audio information signal.

Equipment – AM Transmission Demonstration Experiment

When demonstrating the AM transmission, we used the following equipment including a Oscilloscope this is the apparatus which allows us to view the voltage in the form of waves, displayed on the screen. We also used a function generator, which is used to create electronic waveforms. A wire aerial was involved in our demonstration, as was our AM radio receiver which was the signal for the transmission.

Figure Four

Method – AM Transmission Demonstration Experiment

When demonstrating our AM transmission, firstly we used the function generator to create waveforms electronically. To view this wave we connected the function generator to the oscilloscope, which allowed to us to see the carrier wave and modulated carrier wave, the difference between the two being that a modulated carrier wave can change in relation to position or time. We then connected our AM radio receiver to the circuit in order to pick our AM transmission. This was all completed successfully.

Figure Five

Results– AM Transmission Demonstration Experiment

The results which were concluded from the amplitude modulation transmission demonstration were that the display of the carrier wave and the modulated carrier wave signal on the oscilloscope display were that when we tested the signal with the small radio receiver, and tuned it into the right frequency, the radio made a “buzzing” sound. When we turned off the signal the “buzzing” sound did stop, which has shown that an AM signal had been transmitted.

Explanation of Results – AM Transmission Demonstration Experiment

These results demonstration that we were able to transmit an AM signal and basically we have taken what was firstly a carrier wave and this wave has a set higher frequency and amplitude and which is then generated electronically by an oscillator. Now from this the carrier wave and modulated wave are electronically put together and combined to produce a modulated carrier wave and then the modulated carrier wave will carry this information to be transmitted and broadcasted so that we would be able to hear it through the demonstration.

Conclusion In conclusion this report has explained the two experiments which took place

including the AM radio receiver and audio amplifier experiment and the AM transmission demonstration. In summary the AM radio receiver and amplifier experiment was constructed well as we re-built and soldered parts which were incorrect. Testing the radio receiver was unsuccessful first time round, but from reconstructing the receiver we were able to gain a signal. Also constructing our audio amplifier was a success as we gained a sound from testing our radio receiver with our own speaker system.

In summary of the AM transmission demonstration, the testing the small radio receiver when put through the equipment with the correct frequency the radio produced waves and a “buzzing” noise in which had shown an AM signal had been transmitted through our radio receiver. Even though our radio receiver was not correctly constructed first time round we feel we had solved this issue.

Bibliography

• Figure’s One, two, three, five – “TECH1002-2010-Y STUDIES IN MEDIA TECHNOLOGY (TECH1002_2010_Y) > LEARNING MATERIALS > RADIO LABS > Radio Project: writing the report”

• Figure 4 – Mobile Phone Picture Upload