To construct a working AM Radio Receiver and Audio Amplifier

To understand Radio Waves and how they work

To successfully test both the Radio and Audio Amplifier in the radio lab sessions

AM Radio Construction

For the first part of this experiment, the aim was to build a working AM radio receiver using a kit and instructions from Rapid Electronics. The second part of this experiment was to construct an audio amplifier that would work with the AM radio receiver. In order to determine how successful our radios are, we will test them in labs. However, other factors including reception in the area and the time of day will affect the strength of the signal received by the radio and will have to be taken into account.

·         Rapid Electronics AM Radio circuit board

·         Soldering Equipment

·         Ferrite Rod

·         0.315mm enamelled copper wire

·         Insulating tape

·         IC MK484

·         Transistor BC548B

·         150pF variable tuning capacitor

·         Two 100k resistors

·         Two 1K resistors

·         One 270R resistor

·         Ultra-miniature slide switch

·         Two 100nF capacitors

·         One 10nF capacitor

·         One 47uF capacitor

·         Headphone socket

·         AA battery holder

Both images from Rapid Electronics support notes

·         Rapid Electronics Audio Amplifier circuit board

·         IC TBA 820M

·         Three 1K resistors

·         One IR resistor

·         Two 330uF electrolytic capacitors

·         One 10uF electrolytic capacitor

·         One 150pF ceramic capacitor

·         One 100nF polyester capacitor

·         One 47nF polyester capacitor

·         One 8 ohm speaker

·         100mm of speaker cable

·         On slide switch

·         One PP3 battery snap

·         One 3.5mm plug to plug cable

·         One 3.5mm stereo jack socket Both images from Rapid Electronics support notes

AM Radio Receiver

When building the AM radio receiver, the first step was to gather the components that would be needed to be soldered to the circuit board. When soldering the equipment to the circuit board, it was imperative to ensure that the correct amount of solder was used on each connection. If there was too much colder, then there would be a risk of it touching another connection. If there was not enough solder on each connection, then the connection would not be strong enough and therefore the circuit would not work. The group followed the instructions provided in the Rapid Electronics sheet when deciding the order in which the components should be soldered in place. First, the resistors were soldered, then the smaller capacitors, the BC548B transistor, then the MK484 radio IC, the variable tuning capacitor, the connecting wires to the headphones socket, the headphones socket, the aerial and finally the AA battery holder. Before soldering the aerial in place, it was necessary to remove the enamel from the wire to ensure a good connection was made to the circuit.

Audio Amplifier

The construction of the audio amplifier was very similar to that of the AM radio receiver. Once all of the components were ready, they were soldered to the circuit in the following order; the resistors, the smaller capacitors, the electrolytic capacitors, the LED, the IC socket, the battery connector, the connecting wires to the speaker, the slide switch, the headphone socket and finally the TBA820M.

AM Radio Receiver Results

When the radio was first tested in the radio lab, it failed to pick up any radio stations. The reason for this was found to be a problem with the soldering on the circuit board. On many of the connections, not enough solder had been used, resulting in a weak connection. The connections were then re-soldered and the radio was tested once again. This time it managed to pick up two radio stations, Sabras Radio and the BBC Asian Network. The reception for both stations was quite strong and the audio was clear. However, these were the only two stations the receiver was able to pick up.

Audio Amplifier Results

In order to test the audio amplifier, it was connected to a separate AM receiver that had been used before to ensure that any problems were being caused by the amplifier rather than the receiver. The audio was very distorted and at first this believed to be a problem with the soldering on the amp’s circuit. However, when tested with other radios and audio equipment it was found to be the signal for the radio station.

Explanation of the results

As stated earlier, the AM radio receiver managed to pick up two stations. However, there are many other radio stations operating on the AM frequency locally and nationally. There are many reasons why the radio receiver was unable to receive these. One is that the radio lab in which the radio was tested in is located within a large building consisting of a lot of metal framework and supports. This would have affected the radio as one of the weaknesses of the AM frequency is that it is susceptible to interference from such buildings. Also, being in a large city affects the AM frequency in the same way due to the large amounts of large buildings. The time of day also has an impact upon AM frequency and if the radio had been tested at a different time, it is possible that it would have been able to pick up other radio stations.

Frequency, Amplitude and Wavelength

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum. Their waves are shorter than infrared, visible light, ultraviolet radiation and gamma rays. The aim of the radio waves experiment carried out in the lab was for us all to see the sound waves created on a wave simulator. We then adjusted the frequency to a high or low pitch sound, in order to see the changes in the wavelength and the amplitude. The high pitch, or a high frequency, the sound created is almost like a screaming sound. It’s sometimes unbearable on the ear and very annoying. A low pitch sound or a low frequency is quite flat and is almost a humming sound. This frequency is measured in hertz. The wavelength is the space between each wave and the amplitude is the height of the wave. Large amplitudes give the wave more power and so are louder than a shorter wave. This wave simulator works when you put in the input of sound, its output shows the waves on the screen.

Using Radio Waves

Radio waves have lots of different uses in today’s society. Its main use is in communication, but it is also used in medicine, in small surgical treatments or inn sleep disorders. It’s been used in communication for over a century. The radio works because you hear sounds from the transmitter which the radio station has converted from a sound wave into electromagnetic waves. These waves are at a frequency which is possible for a human ear to listen to, generally around 500-1600 kHz for AM stations or 86-107 MHz for FM stations. These radio electromagnetic waves are used because they can travel very large distances in a short amount of time without being scattered about or absorbed by the atmosphere. This creates a much clearer sound for the radio speaker to omit.

How radio electromagnetic waves are changed to Radio Waves

The sound wave is equivalent to a pressure wave travelling through the air.

A microphone converts the sound wave into an electrical signal.

The electrical wave travelling through the microphone wire is analogous to the original sound wave.

The electrical wave is used to encode or modulate a high-frequency "carrier" radio wave. The carrier wave itself does not include any of the sound information until it has been modulated.

The carrier wave can either be amplitude modulated (AM, top) by the electrical signal, or frequency modulated (FM, bottom).

The signal is transmitted by a radio broadcast tower.

Your radio contains an antenna to detect the transmitted signal, a tuner to pick out the desired frequency, a demodulator to extract the original sound wave from the transmitted signal, and an amplifier which sends the signal to the speakers. The speakers convert the electrical signal into physical vibrations (sound).

The aim of the project was to construct an AM radio and amplifier. The radio was constructed and was also tested to ensure that it worked. It was found that both the radio and the amplifier worked successfully. The radio managed to pick up 2 radio channels, one of which was BBC Radio Asian Network. This shows how the AM radio was a success as we were able to demonstrate that it worked.

The secondary aim was to also understand radio waves and how they work. This was achieved by testing the radio through the equipment in the labs. The group were able to understand how a radio works and how radio waves work by the end of the project.

Overall it can be concluded that the radio was constructed successfully and was shown to work, the group therefore accomplished their goal. Knowledge of radio waves and how they work was increased due to the work which was completed by the group.

References:

http://www.yourdictionary.com/images/computer/WAVELEN.GIF

http://www.nrao.edu/index.php/learn/radioastronomy/radiocommunication

http://en.wikipedia.org/wiki/Radio_waves

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