Elenco AM Radio Kit Manuel d'utilisateur télécharger pdf (Page 32)

Figure 29

DYNAMIC MEASUREMENTS

With the power turned OFF, connect the oscilloscope to

the circuit as shown in Figure 29.

Set the oscilloscope for

a vertical sensitivity of 1 volt/division and turn the power

ON. The oscilloscope should display a low voltage sine

wave. The frequency of the sine wave should change

when capacitor C1 is turned. If your circuit fails this test,

turn the power OFF and check components Q1, C1, C2,

C3, L1 and L2.

OSCILLATOR CIRCUIT

GND TP10

Oscilloscope

FINAL ALIGNMENTS

With the power turned OFF, connect the RF generator and

the oscilloscope to your circuit as shown in Figure 30.

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

Figure 30

GND

TP10

Output Adjust

Generator

Oscilloscope

.02μF

Wire lead

or clip lead

Probe

-31-

GND

TP10

If you do not have an RF generator, go to the Final Alignments with No Test Equipment Section.

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Elenco AM Radio Kit Manuel d'utilisateur Page 32

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