Antenna Alignment - Elenco Electronics AM-550K Assembly And Instruction Manual

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

ANTENNA ALIGNMENT

With the power turned OFF, connect test equipment
to your circuit as shown in Figure 26.
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 27). Change the
Close to
Antenna
Wire Loop
Generator
TP8
Output
Adjust
Set the RF
Figure 26
Wax
Coil
Wax
Figure 27
-27-
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.
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 25). 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 27).
Probe
Holders
Oscilloscope
TP8