Elenco AM/FM Radio Kit - Manual (Page 50)

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Figure 46
AC GAIN
Connect the RF generator and oscilloscope and
oscilloscope to the circuit as shown in Figure 46. The
scope probe must have an input capacitance of 12pF
or less otherwise the probe will detune T2 causing an
incorrect measurement of AC gain. Set the generator
at 10.7MHz no modulation and minimum voltage
output. Set the scope to read 20mV per division and
turn the power ON. Slowly increase the amplitude of
the generator until 3 divisions or 60mVpp are seen
on the scope. With an alignment tool or screwdriver,
adjust T2 for a peak. Reduce the generator input to
maintain 3 divisions on the scope. Move the scope
probe to the base of Q4 and record the input voltage
here:
Vb = __________mVpp.
Turn the power OFF. The AC gain can be calculated
as follows:
AC Gain = 60mV / Vb
Your calculated answer should be about 10.
Record your calculation:
AC Gain = __________
BANDWIDTH
Connect your test equipment as shown in Figure 46.
Set your generator at 10.7MHz no modulation and
minimum voltage output. Set the scope to read 20mV
per division. Turn the power ON and slowly increase
the amplitude of the generator until 60mVpp is seen
on the scope. Increase the frequency of the
generator until the voltage drops 0.707 of its original
value, 2.1 divisions or 42mVpp.
Record the frequency of the high 3dB drop-off point
here:
Fh = ___________MHz.
Decrease the frequency of the generator until the
voltage drops to 0.707 of its original value, 2.1
divisions or 42mVpp. Record the frequency of the
low 3dB drop-off point here:
Fl = ___________MHz.
The bandwidth of the first IF can be calculated as
follows:
Bandwidth = Fh - Fl
Your calculated answer should be between 300 -
500kHz.
Record your calculation:
Bandwidth = __________kHz.
If you don’t have an RF generator and oscilloscope, skip to Section 9.
GND
TP15
Oscilloscope
GND
TP15
Generator
.001 μ F
DYNAMIC MEASUREMENTS