Objectives

1. Transmit and receive EM waves over a short distance
2. Study how various factors affect transmission/reception
   • transmitting/receiving antenna orientation
   • frequency of generating signal
   • distance between antennas
   • connection of antennas to equipment

Resources

• Function Generator
• Oscilloscope
• Banana cables and coaxial->banana cable connectors

Background

An electromagnetic wave carries energy through space in the form of an oscillating electric field and magnetic field. The two fields oscillate perpendicular to each other and perpendicular to the direction of wave travel. EM waves can be produced by a single oscillating charge, as shown in this simulation, or by the oscillation of multiple charges in a wire carrying alternating current.

Setup

Connect a wire to the positive output of the function generator (use a coaxial adapter if necessary) and leave the other end free. Using a second coaxial adapter, connect a wire to the positive side of channel one of the oscilloscope and leave the other end free as well.

Lay the two free ends of wire near each other on the table and set the function generator to produce a signal with a frequency in the range of 10-1000 kHz. Pressing the AUTOSETbutton on the oscilloscope will allow it to determine approximately the best settings for viewing the incoming signal. The vertical and horizontal scales can then be adjusted using the VOLTS/DIV and SEC/DIV controls, respectively.

Analysis Questions

1. While maintaining a distance of >1cm between the two wires, what arrangement of the two wires produces the strongest received signal? Why do you think this is?
2. How does the strength of the received signal change with distance between the two wires? Explain your method for finding this.
3. Is there any frequency dependence on the strength of the received signal? Why do you think this might be?
4. Try using different types of signal to generate the EM wave (i.e square, triangle waves). How does this affect the output and why?
5. What if you connect one or both of the wires to the grounded side of the output and/or input? Can you explain this?