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ANTENNA ALIGNMENT
Tune the radio for a station around 600kHz. With the
"magic wand" place the brass end near the antenna coil
as shown in Figure 23. If the signal heard at the output
increases, it means that the antenna coil needs less
inductance. To remove inductance, carefully slide the
antenna coil along it's ferrite core in the direction shown
in Figure 23. Place the iron end of the "magic wand"
near the antenna coil. If the signal heard at the output
increases, this means that the antenna coil needs more
inductance. To add more inductance, carefully slide the
antenna coil along its ferrite core in the direction shown
in Figure 23. Repeat these steps until the signal heard
decreases for both ends of the "magic wand". Tune the
radio for a station around 1400kHz. With the "magic
wand", place the brass end near the antenna coil. If the
signal heard at the output increases, it means that the
antenna coil needs more capacitance.
antenna trimmer on the back of the gang until the signal
is at its loudest. Refer to Figure 25 for the location of
the antenna trimmer. Place the iron end of the "magic
wand" near the antenna coil. If the signal heard at the
output increases, it means that the antenna coil needs
less capacitance. Adjust the antenna trimmer on the
back of the gang until the signal is at its loudest.
Repeat these steps until the signal heard decreases for
both ends of the "magic wand". Since the adjustment of
both the antenna trimmer and antenna coil will effect
the antenna alignment, it is advisable to repeat the
entire procedure until the antenna alignment is
optimized. This process sets the tracking of the AM
radio section. Once the antenna is properly aligned,
AM ALIGNMENT WITH TEST EQUIPMENT
IF ALIGNMENT
Connect your RF generator and oscilloscope as shown
in Figure 24. Make sure that the switch is in the AM
Figure 24
Generator
.001µF
Hz
TP15
Adjust the
Short TP6 to the collector Q7.
CAREFULLY APPLY CANDLE WAX or glue to the
antenna coil and the ferrite rod to prevent it from
moving (see Figure 23A).
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 108T. 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.
Magic Wand
Antenna
Shim
If the antenna needs:
• More inductance, slide the coil
• Less inductance, slide the coil
Wax
Wax
position. Place a short from the collector of Q7 to TP6.
This short "kills" the AM oscillator.
-28-
Antenna Coil
Ferrite Core
Antenna Holder
Figure 22
Figure 23
Oscilloscope
TP15
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