Elenco SEE AMFM108CK - Manual (Page 29)

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Set the RF generator at 455kHz, modulation of
400Hz 80% and minimum voltage out. Set the
oscilloscope to read .1 volts per division and turn the
power ON. Increase the amplitude of the generator
until the oscilloscope shows a 400Hz sinewave 5
divisions or .5 volts pp. With an alignment tool or
screwdriver adjust T6 for a peak. Reduce the
generator amplitude so that 5 divisions are
maintained. Adjust T7 for a peak and reduce that
amplitude again if necessary. Repeat these steps to
optimize the IF alignment. This process aligns the IF
amplifiers to 455kHz.
After the IF alignment is complete, lower the
frequency of the generator until the voltage drops
.707 of its peaked value or .35Vpp. Record the
frequency of the lower 3dB corner here:
Fl = _________kHz.
Increase the frequency of the generator past the
peak until the voltage seen on the scope drops .707
of its peaked value or .35Vpp. Record the frequency
of the high 3dB corner here:
Fh = __________kHz.
The bandwidth of the IF is equal to BW = Fh - Fl. The
IF’s bandwidth should be around 6kHz. Turn the
power OFF and remove the short from the
collector of Q7 to TP6.
Calculate the bandwidth: __________kHz.
OSCILLATOR ALIGNMENT
Set the RF generator at 540kHz, 400Hz 80% AM
modulation and a low level of output. Turn the power
ON and set the volume control to a comfortable level.
Turn the tuning knob counter-clockwise until the
white pointer is aligned at the 540kHz marking on the
dial. With an alignment tool or screwdriver adjust L5
until a 400Hz tone is heard. Adjust L5 for a peak on
the oscilloscope. Adjust the amplitude of the RF
generator to maintain a level of .5 volts peak to peak
or less. After peaking L5, set the generator
frequency to 1600kHz. Turn the tuning knob
clockwise until the white pointer is aligned to the
1600kHz marking on the dial. With an alignment tool
or screwdriver, adjust the AM oscillator trimmer on
the back of the tuning gang until a 400Hz tone is
heard. Adjust the trimmer for a peak on the
oscilloscope. Refer to Figure L for the location of the
AM oscillator trimmer. Repeat these steps to
optimize the oscillator alignment. This process sets
the oscillator range at 955kHz to 2055kHz.
ANTENNA ALIGNMENT
With the power turned OFF, connect your test
equipment as shown in Figure 25.
Figure 25
Battery
Generator
Hz
TP15
Wire loop
close to
antenna