Elenco Electronics AM-550TK Instruction Manual download pdf (Page 28)

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Figure 21

.02μF

Output

Adjust

Oscilloscope

Generator

Clip Lead

GND

Probe

Antenna Trimmer

Oscillator Trimmer

Antenna Trimmer

3 Leads 4 Leads

Figure 22

FINAL ALIGNMENTS

With the power turned OFF, connect the RF generator

and the oscilloscope to your circuit as shown in Figure 21.

Short TP2 to the collector of Q1 with a clip lead to “kill”

the local oscillator. Set the RF generator at a frequency

of 455kHz, modulation of 400Hz 80%, minimum

amplitude output. Set the oscilloscope to read 0.1Vpp

and turn the power ON. Increase the amplitude of the

RF signal until the oscilloscope registers 0.5Vpp. Align

transformers T3, T2 and T1 for the maximum AC

reading on the oscilloscope. Decrease the amplitude of

the signal from the RF generator to restore 0.5Vpp on

the oscilloscope. Repeat the last two steps until no

change in the peak at the oscilloscope is noticed.

After IF alignment, lower the frequency from the RF

generator until the reading on the VOM drops to 0.707

of its peaked value. Record the frequency of this lower

3dB corner here:

Fl=____________kHz.

Increase the RF generator frequency past the peak to

the upper 3dB corner and record that frequency here:

Fh=____________kHz.

The bandwidth of the IF amplifiers is BW=Fh - Fl. IF

bandwidth should be between 1 to 2kHz. This

bandwidth will widen as the AGC is approached.

IF BANDWIDTH

With the power turned OFF, connect the equipment to

the circuit as shown in Figure 21. DO NOT connect the

clip lead from TP2 to Q1. Set the RF generator at

540kHz, 400Hz 80% modulation, and a low level of

output. Turn the tuning capacitor fully counter-

clockwise. Turn the power ON and a 400Hz tone should

be heard coming from the speaker. Tune the oscillator

coil (L2) for a peak on the oscilloscope. Adjust the RF

generator output during this process to maintain a peak

at 0.5Vpp or less. After peaking L2, set the RF

generator frequency to 1600kHz and turn the tuning

capacitor (C1) fully clockwise. A 400Hz tone should be

heard coming from the speaker. Tune the oscillator

trimmer capacitor on the back of C1 for a peak on the

oscilloscope (see Figure 22).

SETTING OSCILLATOR RANGE

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Elenco Electronics AM-550TK Instruction Manual Page 28

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