Introduction During the Studies in Media Technology labs we have been asked to produce a fully functional AM radio. The following is a lab report of the whole process including; methodology of production, testing and notation of each lab. Before the radio was actually produced a lot of research into the technology and science behind the AM radio had to be understood, this includes the nature of electromagnetic waves, the technologies involved in receiving EM waves and also the technologies in transmitting information using EM waves. The overall aim of the project was to gain an in depth understanding of not only how the technology works and the science behind it, but to be able to produce and make use of an AM Radio.
AM Radio Receiver Production First of all, get a roll of copper wire 0.315mm in diameter or wire gauge of 30 s.w.f, measure out 2.5m and cut off of the roll with standard wire cutters. Place a small cardboard tube over the ferrite rod allowing the coils to be moved at will up and down the rod. Tightly wrap copper wire around the cardboard of the ferrite rod; it must be 55 turns around the rod which should work out to a coil of approximately 25mm in width. Note: Ensure each turn of the copper wire coil do not overlap each other as this could affect the quality of reception. At either end of the coil, tape it down to ensure no overlapping or un-coiling occurs, this will secure the coil in place. Next start by soldering each resistor in its correct place on the circuit board, following the diagram provided above to ensure correct placement. Solder the smaller capacitors into the correct place; the 10nF should be soldered in the position of C1 in the diagram. Next the two 100nF capacitors should be soldered into C3 and C4 positions. Solder the BC548B transistor into place. Solder the MK484 IC into place. Solder the variable tuning capacitor into position. Next strip the end of the plastic cover around two connecting wires off. Then attach the stripped ends to the headphone socket, solder them in place. Strip the opposite ends of the wires and then solder those into the correct position on the circuit board. Use the sand paper to sand off the enamel coating on the bottom of the aerial copper wire. Next solder these wires into the correct position on the circuit board. Finally attach the battery holder to the circuit board and insert one AA battery.
Audio Amplifier Production Solder each resistor in its correct place, following the diagram above, ensure that no solder is touching otherwise it may short the circuit Now solder the smaller capacitors; C2, C4 and C5 Solder the larger electrolytic capacitors into the correct position; C1, C3 and C6 Solder the LED into position Solder the IC socket into position Solder any remaining external components, like the 8 ohm speaker Place the TBA820M into the IC socket Attach battery and test the circuit
Results Only two AM Radio Transmissions were received: BBC Asian Network 837kHz Sabras Radio 1260kHz
Science and Theory Electromagnetic Waves An Electromagnetic Wave or EM Wave for short, is basically a phenomenon. It is a self propogating wave of energy consisting of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction in which the wave is travelling. EM Waves can be classified into several types according to the waves frequency. Type Radio Microwave Infra-red Visible Ultra-violet X-rays Gamma rays Wavelength range >o.1m 0.1m to 1mm 1mm to 700nm 700nm to 400nm 400nm to 1nm <1nm <1nm All EM Waves travel at the speed of light, c, in a vacuum which is 3x108 ms-1 but also can travel through matter EM Waves were predicted in 1862 by James Clerk Maxwell.
What is an AM Radio Signal? An AM Radio Signal is a wave signal at a frequency in the range of radio that is broadcast using amplitude modulation equipment, thus giving it the name AM Radio. AM Radio Signals can be split into 3 main types: Long Wave - 148.5kHz - 283.5kHz (Europe, Africa and parts of Asia) Medium Wave - 520kHz - 1,610kHz (The Americas) Short Wave - 1.711MHz - 30.0MHz (Commonely used for channel spacing)
Conclusion The aims of this assignment were to understand the sciences involved in AM Radio Reception and also the techniques involved in building an AM Radio Receiver and Audio Amplifier.