Elenco Electronics SUPERHET AM-550TK, Assembly And Instruction Manual

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Figure 23
Figure 24
Wax
Holder Coil
Wire Loop
Close to
Antenna
Probe
Output
Adjust
Oscilloscope
Generator
GND
R6
With the power turned OFF, connect test equipment to
your circuit as shown in Figure 23. Set the RF generator
at 600kHz, 400Hz 80% modulation, moderate signal
strength. Set the oscilloscope to read .5Vpp and turn the
power ON. Turn C1 fully counter-clockwise, then slowly
turn C1 clockwise until a 400Hz tone can be heard
coming from the speaker. Slowly slide the antenna coil
back and forth on the ferrite rod to obtain a peak on the
oscilloscope. For maximum signal, your location of the
antenna coil may have to be on the end of the ferrite rod
(as shown in Figure 24). Change the frequency of the RF generator to 1400kHz and adjust C1 until a 400Hz tone
can be heard coming from the speaker. Carefully peak
the reading on the oscilloscope by adjusting the
frequency of the RF generator. Now tune the antenna coil
to this frequency by adjusting the antenna trimmer on the
back of C1 (see Figure 22).
This process should be
repeated until both settings of the antenna track the
oscillator tuning. Once the antenna is properly aligned,
carefully apply candle wax or glue to the antenna coil and
ferrite rod (as shown in Figure 24).
ANTENNA ALIGNMENT
After peaking the oscillator trimmer capacitor, return the
RF generator to 540kHz, and capacitor C1 to the fully
counter-clockwise position and readjust L2. Repeat the
last few steps until both settings of the oscillator are
correct.
This process sets the oscillator range at
995kHz to 2055kHz. If a frequency counter is available,
you may verify this alignment by measuring the
frequency at the emitter of Q1 for both ends of the
tuning capacitor (C1). Be careful not to mistune the
oscillator during this measurement.
A coupling
capacitor of 82 picofarads or less to the frequency
counter is recommended.