Elenco AM/FM Radio Kit - Manual (Page 13)

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Figure 9
AC BANDWIDTH
Connect the oscilloscope and audio generator to
your circuit as shown in Figure 9. Set the audio
generator for a frequency of 1kHz and minimum
voltage output. Set the oscilloscope to read 0.5 volts
per division. Turn on the power and slowly increase
the volume control to a comfortable level. Increase
the amplitude of the audio generator until the
oscilloscope displays 2 volts peak to peak, (Vpp), at
TP1. It may be necessary to adjust the volume
control. Move the oscilloscope probe to jumper J3
and record the input voltage here:
Vin = _______ Vpp
(at this point, you may want to verify the AC gain).
Move the oscilloscope probe back to TP1 and slowly
increase the frequency from the audio generator until
the waveform on the oscilloscope drops to 0.7 of its
original reading 1.4Vpp or 2.8 divisions. The
frequency of the generator when the output drops to
0.7 of its original value is called the high frequency 3
decibel (dB) corner. Record this frequency here:
(f high 3dB) = __________ kHz.
Slowly decrease the frequency of the generator until
the output drops to 0.7 of its original reading, 1.4Vpp
or 2.8 divisions. This frequency is called the low
frequency 3dB corner. Record your answer.
(f low 3dB) = __________ kHz.
Calculate the AC bandwidth:
(f high 3dB – f low 3dB) = __________ kHz.
AC Bandwidth = __________
Your calculated answer should be greater than
30kHz.
DISTORTION
Connect the generator and oscilloscope as shown in
Figure 9. Set the generator at a frequency of 1kHz,
turn the power ON. Adjust the generator output and
turn the volume until the peaks of the sinewave at
TP1 are clipped for maximum signal as shown in
Figure 10. One side of the sinewave may clip before
the other depending on the DC centering at TP1. If
oscillations are seen, connect a clip lead from the
GND of your generator to the GND of the circuit.
Measure the maximum voltage peak to peak when
clipping first occurs and record that value here:
Vclp = _______ Vpp.
Turn the power OFF.
If an oscilloscope is not available, skip the following test and go directly to Section 1B.
GND
TP15
Oscilloscope
GND
TP15
Generator
Battery