Radio Wave Transmission and Receiving Activity

Pre Lab:

1) List some of the frequencies of your favorite AM or FM radio stations? Are the frequencies expressed in Hz, kHz or MHz?

2) Listen to some local AM and FM radio stations. Do the AM signals sound different from the FM signals? If so, how?

3) Using an AM radio, record the number of strong stations you can hear during the day. These are called groundwaves. Repeat at night . ( these are called groundwaves and skywaves combined) Are there differences in the numbers. Why?

4) Listen to an AM radio at night. Write down the locations of the different stations you hear. What is the farthest station you heard? Repeat for an FM. Is there a difference? Why?

Lab One: The effects of total shielding

Materials: A portable radio, AM or FM or both, a roll of aluminum foil

1) Turn on the radio and pick up a strong station in your area.

2) Wrap the foil around the radio leaving no openings. See how much you have to open the foil before you hear something.

3) Touch the antenna and try it again. Record your results.

Lab Two: The AM Radio

Materials: A portable radio, AM or FM or both, various plugged in appliances

1) Carry your portable AM radio around your house, near your thermostat, lamp dimmers, blender, vacuum cleaner, etc. Record the difference between battery operation and plugged in operation.

2) Use your car's AM radio, or take your portable radio with you while you walk. Record any see sources of local noise.

3) Can you find any “dead” spots (no signal at all?)? Why do you think there is no signal at that particular location?

Lab Three: Radio Frequencies

Materials: HF receiver

1) Over the course of several days, listen for radio signals on at least 5 frequencies between 1 and 30 Mhz. Listen in the morning, afternoon, evening, and after dark on each frequency.

2) Prepare a table showing how readable the signal was on a scale of 1 to 5, with 5 being the most readable. Record the strength of the signal on a scale of 1 to 10, with 10 being the strongest.

3) Use this data to explain how the signals varied with time of day and frequency.

Lab Four: Radio Waves and Distance

Materials: HF receiver

1) Divide the HF bands into 2 MHz bands ranging from 2 to 30 MHz.

2) Listen on each band in the morning, afternoon, evening, and night.

3) Create a table which records whether you are hearing long distance stations, short distance stations or no stations at all.

4) Explain how different bands can be used at different times of the day over different distances.

Lab Five: Your Car Engine

Materials: A portable radio, AM or FM or both, a working car

Explore the radio environment around your own car

1) Bring an AM radio near a running car with the hood closed and with the hood open. Be careful when the hood is open! Do not put your hands inside the engine compartment when the motor is running. Do not allow the antenna to get closer than 6 inches to any high voltage wiring. Record your results.

Lab Six: Radio Interference

Materials: A stereo, HF transceiver, 400-600 ohm resistor

1) Connect a stereo to the same outlet that powers the HF transceiver.

2) Tune in different bands and see if they interfere through the power line.

3) Disconnect the CD player, tuner, or tape player. Leave and see if the transceiver interferes. Record your results. Place a 400-600 ohm resistor on the input. What happens?

Lab Seven: Radio Waves

Materials: Cordless phone, HF transceiver

1) Turn on the HF transceiver and see the effects it has on your telephone reception. Record your results and compare them to your classmates’.

2) Take data at different distances and record how quickly the interference disappears.

Lab Eight: Phase

Materials: Small pan or shallow dish, water

1) Fill a round pan or bowl halfway with water.

2) Place your index finger vertically in the water at the center of the pan and vibrate it up and down rapidly enough to make a steady pattern of ripples in the pan.

3) Observe the pattern of ripples. Draw your results.

4) Move your finger to another location about halfway to one edge of the container and repeat. Record the pattern of reflected ripples and any points where the ripples seem to add or cancel.

5) Use both your index fingers a few ripple-lengths apart and make a pattern of ripples. Can you see the ripples adding and subtracting? (Another way to create two sets of ripples is to use a pair of pencils taped to a ruler.) Try to make your fingers move in-phase (up and down at the same time) and out-of-phase. How does this relate to the radiated field from two antennae?

Post Lab:

1) Look around your neighborhood. And record the number of different antennas you see. Be sure to note the different styles of antennas as well.

2) Look around your town. Record how many antenna towers you see as well as their locations. Try to guess what each is used for.