ELEC 241 Lab

Testing

Self Test.

If each component of your system has passed the test given in its construction section, then your system should be functional. Because the antenna is switched between the transmitter and receiver, and because it is not possible to run both the transmitter and receiver VIs at the same time, it is not possible to test both parts of the system simultaneously. However, we can verify that both halves are functioning properly by using a second antenna connected to either the oscilloscope or the function generator.

Get two antennas. Connect one to the Antenna Interface and the other to the oscilloscope. Place the two antennas close to each other. Set the switch on the Antenna Interface to transmit. Connect the function generator and set it to produce a 1 kHz 1 V sine wave. Start the Transmitter VI. You should see an AM modulated signal on the scope.

Disconnect the function generator. Speak into the handset microphone in a normal voice and verify that full modulation is being achieved. If not, adjust until it is. Plug in the dynamic microphone. Speak into it and adjust if necessary to achieve full modulation.

Stop the transmitter VI. Remove the antenna from the oscilloscope and connect it to the function generator. Set the function generator frequency to 174 kHz. Set the switch on the antenna interface to Receive. Start the receiver VI. You should hear a 1 kHz tone from the earphone.

Full System Test.

The maximum range you can achieve in a self test is limited by the length of the antenna cable to about 5 feet. Since the specifications call for a range equal to the length of the lab (about 50 feet) you will need the cooperation of another lab group to perform a full system test.

Find another lab group to work as your partner for full system testing and characterization. If there are an odd number of groups, one of the labbies will serve as your partner. First verify that your systems work together at short range (e.g. at the same or adjacent lab stations).

The full range test is very simple: with you and your partner group at the two test stations, you should be able to carry on an intelligible, two-way (half-duplex) conversation.

Although the antennas we are using are not highly directional in the sense that they do not produce a narrow beam, they are directional in the sense that they are more sensitive in some directions than others. This means that successful communication over long distances will require attention to orientation of the antennas. This may require a compromise between maximizing the received signal (with the transmit and receive antennas coplanar) and minimizing interference.

Since other groups may be trying to communicate at the same time you are, there is potential for interference. Since we have a 30 kHz band available and a speech signal has a bandwidth of only about 3 kHz, there are a number of different channels available.