Elenco AM Radio Kit - Manual (Page 24)

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DYNAMIC MEASUREMENTS
Turn the power OFF and connect the VOM and RF
generator as shown in Figure 21. Set the VOM to
accurately read 2 volts DC and set the output of the RF
generator for 455kHz, no modulaton, and minimum
amplitude. Turn the power ON and slowly increase the
amplitude of the 455kHz signal from the RF generator until the voltage at TP3 just starts to drop. This point is
called the AGC threshold with no IF gain. Make a note
of the amplitude setting on the RF generator here:
____________.
Turn the power OFF.
DETECTOR AND ACG TEST
If your RF generator does not have amplitude modulation or you do not have an oscilloscope, go to Section 3.
Connect equipment as shown in Figure 22.
Set the RF generator at 455kHz, 1kHz at 80%
modulation and minimum output. Turn the power ON and
put the volume control at full clockwise position. Slowly adjust the amplitude of the RF generator output until you
hear the 1kHz on the speaker. If this test fails, turn the
power OFF and check C11, R12, volume control, D1 and
TP3.
SYSTEM CHECK
Connect equipment as shown in Figure 22. Set the RF
generator at 455kHz with 80% modulation at a
modulation frequency of 1kHz. Set the oscilloscope to
read 0.1 volts per division. Turn the power ON and put
the volume control at minimum. Increase the amplitude
of the RF generator until the signal on the oscilloscope
is 4 divisions peak to peak. Check the signal to make
sure it is free of all distortion. Leave the frequency of the RF output at 455kHz, but increase the modulation
frequency until the output drops to 0.28 Vpp. Record the
modulation frequency on the RF generator here:
_________.
This frequency should be greater than 5kHz. Turn the
power OFF.
DETECTOR BANDWIDTH TEST
Figure 21
GND
TP10
.02
μF
GND
TP10
Output Adjust
Generator
Figure 22
.02 μF
GND
TP10
Output Adjust
Generator
GND
TP10
Oscilloscope
Probe