Antenna Activities: Wireless Internet Directional Antenna

After completing some of the pre-existing antenna activities, students can try the following, originally intended as a directional antenna for a wireless internet hub. The resulting antenna should be more focused in direction than the default dipole antenna and thus travel considerably further. Note that by using this particular configuration, the wireless will broadcast best on channel 6 or at a frequency of 2.437 MHz. This activity is adapted from Wi-Fi Toys by Mike Outmesguine.

Materials needed:

Coffee Can (Maxwell house and Folgers Coffee work well)

Approx. dimensions:

Diameter: 100mm

Length: 123 mm

Drill

Coax cable

N-Connector for coax cable

Round copper wire or pole (core conductor from coax cable works well)

Approx. dimensions:

Length: over 31 mm

Diameter – same as the core conductor from coax cable

1. Empty and clean the can – make sure the opening is completely smooth.

2. 44 mm up from the interior bottom of the can drill a single hole

3. Make the correct size for your N-Connector and file away any rough edges

4. Slip your round pole (the radiating element) into the N-Connector opening. Light sanding may be necessary to fit it in. Solder the connection.

5. Measuring from the end of the connector jack, trip your radiator down to 30.7 mm

6. Mount the N-Connector to the hole in the side of your can with the radiating element inside the can. Trim down any overly protruding screws on the inside of the can.

7. Connect the can with your coax cable to your internet receive or transmitter.

Follow-up Questions:

1. Test the transmission range and directional sensitivity of your wireless internet before the additional of the can antenna.
2. Retest the same criteria after the addition of the can.
3. Compare the change and related this to the size and orientation of the can antenna.
4. Why is the length of the radiating element and the length of the can and the position of the radiator so precisely determined? (hint: calculate the wavelength of the microwave radiation)

Antenna Activities: Wireless Coax Cable Signals

The fact that a signal is transmitted from a VCR to a TV via the coax cable is easily demonstrated by cutting the coax cable while viewing a recording on the TV.

The signal of the coax cable can radiate like an antenna however. By attaching the central wire on either side of the cut coax cable to a short piece of conducting material, the signal can be restored without reconnecting the cable.

Variation of the demonstration:

1) Show that the signal transmission degrades quickly as the ends of the coax cable with their attached conductors are separated. Discuss why this happens?

2) Is the signal quality dependent on the relative orientation of the two conductors? Is the wireless signal polarized?

3) What kind of effects can be observed by placing other objects (conductors and non conductors) near or in the middle of the transmission area.

Have the students write down their observations and relate as many of their observations to the recent lecture on waves in motion.

Antenna Activities: Wireless Interfering Signals

Wireless internet and microwaves and some cordless phones all operate at the same microwave frequency.

Have the students make observations either in school or at home by monitoring the data transmission rate from their wireless internet connection. They should find the ‘dead’ or weak spots in their house. They should discover the limits of reception.

These measurements could be highly sensitive to the placement and use of other household microwave using devices (such as the microwave oven and cordless phone). Other, built in metallic materials may be reflecting or absorbing the signal as well.

Make multiple measurements at some positions while using the cordless phone and/or the microwave.

Explain your observations by using the physics of wave propagation.