Elenco SEE AMFM108CK - Manual (Page 39)

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AC GAIN
Connect the RF generator and oscilloscope to the
circuit as shown in Figure 35. The scope probe must
have an input capacitance of 12pF or less otherwise
the probe will detune T3 resulting in a false reading
of the AC gain. Set the generator at 10.7MHz no
modulation and minimum voltage output. Set the
scope to read 50mV per division and turn the power
ON. Slowly increase the generator until 150mVpp or
3 divisions are seen on the scope. With an alignment
tool or screwdriver adjust T3 for a peak. Reduce the
generator until 150mVpp or 3 divisions are seen on
the scope. With an alignment tool or screwdriver
adjust T3 for a peak. Reduce the generator input to
maintain 3 divisions on the scope. Move the probe to
the base of Q5 and record the input voltage here:
Vb = __________ mVpp.
Turn the power OFF. The AC gain can be calculated
as follows:
AC Gain = 150mV / Vb
Your calculated answer should be about 20.
Record your calculation:
AC Gain = __________
BANDWIDTH
With the power turned OFF, connect your test
equipment as shown in Figure 35. Set your
generator at 10.7MHz no modulation and minimum
voltage output. Set the scope to read 50mV per
division. Turn the power ON and slowly adjust the
generator amplitude until 150mVpp is seen on the
scope. Realign T3, if necessary, for maximum output
while adjusting the generator to maintain 150mVpp.
Slowly decrease the frequency of the generator until
the voltage drops .707 of its original value, 2.1
divisions or 106mVpp. Record the frequency of the
lower 3dB drop-off point here:
Fl = _________MHz.
Increase the frequency until the voltage drops to .707
of its original value, 2.1 divisions or 106mVpp.
Record the frequency of the high frequency 3dB
drop-off point here:
Fh = ___________MHz.
The bandwidth of the 2nd IF can be calculated as
follows:
Bandwidth = Fh - Fl
Your results should be between 300 - 500kHz.
Record your calculation:
Bandwidth = __________
Figure 35
TP15
GENERATOR
Hz
TP15
.001 μ F