Instruction manual

AC Test

If you do not have a signal generator, skip to

procedure 4.

Make sure that the power switch is in the OFF

position. Turn the squelch control fully

counterclockwise . Set the mulitmeter to read

20VDC full scale and connect to the circuit as

shown in Figure 21. Connect the positive voltage

probe to pin 13 of integrated circuit U1. Connect the

common probe to the negative lead from the battery.

AC couple a generator capable of producing a

455kHz signal to pin 5 and attach the generator

ground lead to the ground lead of the volume control

(see Figure 21). Set the generator frequency to

455kHz and the amplitude to between 50 and

100mV peak to peak. Turn the power ON. Turn coil

L5 to its maximum counterclockwise position. The

multimeter should read approximately 2.4V. Turn L5

slowly clockwise. The multimeter voltage should

rise to a maximum of about 3.0V, then fall to a

minimum of about 1.5V and then rise again. Record

the maximum (Vmax) and minimum (Vmin)

voltages. Set L5 midway between Vmax and Vmin.

For example, if Vmax = 2.95V and Vmin = 1.45V, set

L5 to (Vmax + Vmin)/2 = (2.95 + 1.45)/2 = (4.40)/2

= 2.2V.

A small increase in generator frequency (positive

deviation) should cause the DC voltage at pin 13 to

drop. Likewise, a small increase in generator

frequency (positive deviation) should cause the DC

voltage to rise. Careful point-by-point plotting (use

increments of about 1kHz) should reproduce a

curve similar to the one shown in Figure 16. If not,

turn the power OFF and check that the 455kHz filter

F1 is installed correctly. Also check for solder

shorts, unsoldered leads, and parts you may have

missed in the block 2 assembly instructions.

-17-

Figure 21

COM

ΩΩ

104

455kHz

20A