Elenco SEE AMFM108CK - Manual (Page 30)

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Set the generator at 600kHz, 400Hz 80%
modulation, moderate signal strength. Set the
oscilloscope to read .1 volts per division. Turn the
tuning knob fully counter-clockwise and turn the
power ON. Slowly turn the tuning knob clockwise
until a 400Hz sinewave is seen on the scope. Adjust
the volume control to a comfortable level. If a station
exists at 600kHz, then lower the frequency of the
generator and repeat the previous steps. With the
“magic wand”, place the brass end near the antenna
coil as shown in Figure 22. If the signal on the scope
increases, it means that the antenna coil needs less
inductance. To add more inductance, carefully slide
the antenna coil along it’s ferrite core in the direction
shown in Figure 22. Repeat these steps until the
signal seen decreases for both ends of the “magic
wand”. Increase the frequency of the generator to
1400kHz and turn the tuning knob clockwise until a
400Hz sinewave is seen on the scope. If a station
exists at 1400kHz, increase the frequency of the
generator and repeat the previous steps. Place the brass end of the “magic wand” near the antenna coil.
If the signal increases, it means that the antenna coil
needs less capacitance. Adjust the antenna trimmer
for a peak. Refer to Figure L for the location of the
AM antenna trimmer. Since the adjustment of both
the antenna alignment is optimized. This process
sets the AM tracking of the Superhet 108.
Once the antenna is properly aligned, carefully apply
candle wax or glue the antenna coil to the ferrite rod
to prevent it from moving as shown in Figure 23. Cut
the shim flush with the antenna. Proceed to the FM
assembly section.
This concludes the alignment of the AM radio
section. If no stations are heard, verify that AM
signals are present in your location by listening to
another AM radio placed near the Superhet 108. If
the AM section is still not receiving, go back and
check each stage for incorrect values and for poor
soldering. Proceed to the FM assembly section.
1. The number of vibrations (or cycles) per second
produced by a sound is called the frequency, and
is measured in hertz.
2. The distance between peaks of sound waves is
called the wavelength.
3. Sound waves are produced as a certain number
of vibrations per second. The more vibrations per
second, the higher the frequency; the fewer
vibrations, the lower the frequency.
4. Waves of very high frequency are called radio
waves and travel great distances through the air
without the use of wires.
5. Carrier waves are radio waves used by broadcast
stations to carry audio waves.
6. The process of adding the audio waves to the
radio waves is called modulation, and the
process of removing the radio wave from the
audio wave is called demodulation, which is
performed in an AM radio by the detector.
7. The amount of signal picked up by the antenna
will depend on the power of the signal transmitted
and the distance the signal travelled.
8. Rectification is the process of removing half the
signal, while filtering is the process of smoothing
that signal.
9. Heterodyning is the process of mixing two signals
(the incoming RF signal and the RF signal from
the local oscillator) to produce a third signal (the
IF signal).
DC VOLTAGES
Q7 B 1.5 U1 1 1.3
E 1.0 2 0
C 8.8 3 0
4 0
TP5 (AGC) 1.4 5 4.5
6 9.0
Q8 B 1.4 7 4.6
E .8 8 1.3
C 8.8
Q9 B 1.7 TP1 4.5
E 1.0
C 9.0
Test Conditions
1. Volume set to minimum.
2. Connect side of capacitor C29 (that goes
to L4) to TP15 with a jumper wire.
3. Battery voltage = 9V
4. All voltages are referenced to circuit
common.
5. Voltage readings can vary +10%
AM RADIO HIGHLIGHTS
The voltage readings below should be used in troubleshooting the AM section. (Switch at AM position).