ELEC 241 Lab

Characterization

When your system (and your partner group's) has passed the full range test, you should characterize it by getting quantitative performance characteristics at three different ranges: 5 ft, 10 ft, and 50 ft. Characterization will consist of 2 pairs of measurements made at each of the 3 ranges (a total of 2 x 2 x 3 = 12 measurements).

Preparation.

Set the function generator to produce a 1 kHz sine wave. Unplug the dynamic microphone and the handset. Adjust the function generator amplitude to produce a fully modulated signal. With your DMM set to AC volts, measure and record the function generator output voltage. Set the volume control to maximum loudness.

Procedure.

At each test distance perform the following procedure. At the receiving end turn off the function generator. Point your receiver antenna at your partner group's transmitter. Carefully orient the receiver antenna for maximum received output. Also orient the transmitter LED or move the position of the receiver antenna so that the receiver is in the brightest portion of the transmitter beam (finding the brightest part of the beam is best done by eye). Measure the RMS value of the receiver output, $v_{ro}$ . You must use a true RMS meter for this measurement, not your DMM or scope. You may borrow one from the shop or use the "Simple Digital Multimeter" Labview program. This is the signal plus noise voltage.

Without moving the receiver antenna, have your partner group cover the LED, blocking the beam. Again measure the RMS value of $v_{ro}$ . This is the noise voltage. Compute the signal plus noise to noise ratio

$\displaystyle 20\log_{10}\left(\frac{v_{s+n}}{v_n}\right)$

Repeat these two measurements using your system as the transmitter and your partner group's as the receiver. Record both sets of measurements. Repeat these measurements at the two other test distances.

Note: Be sure that the function generator is turned off at the receiving end for all measurements.