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, 15 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 disconnect the function generator.
Carefully orient the
transmitter and
receiver antennas for maximum received output.
Measure the
RMS
value of the receiver output.
If you are using the prefabricated receiver VI,
there is a display of the RMS value of the demodulated output
in the lower left corner.
If you have made your own receiver, you can add an RMS display
using the
Amp and Level
block from the
Signal Analysis
palette.
Or you can measure the voltage 
at the output of the earphone driver.
In this case
you must use a true RMS meter
(available from the shop)
for this measurement, not
your DMM or scope.
The voltage you measure will be the
signal plus noise
voltage.
Without moving either antenna, have your partner group
switch their antenna interface to
Receive.
Again measure the RMS value of
the receiver output.
This is the
noise
voltage.
Compute the
signal plus noise to noise
ratio
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
disconnected
at the receiving end for all measurements.