Elenco Electronics AM/FM-108CK, Сборка и инструкция по эксплуатации

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SECTION 7
Figure 34
10.625MHz 10.775MHz
10.7MHz
.707
METHOD #2
ALIGNMENT OF RATIO DETECTOR USING A
RF GENERATOR AND OSCILLOSCOPE
Connect the RF generator and oscilloscope to the
circuit as shown in Figure 32. Set the generator for
10.7MHz modulated at 1kHz, 22.5kHz deviation with
minimum voltage out. Turn ON the radio and turn the
volume control to the minimum. Slowly increase the
amplitude of the generator until a 1kHz sinewave is
seen on the scope. With an alignment tool or
screwdriver, peak the pink coil T4 for maximum
amplitude. Now peak the blue coil T5 for minimum
optimized. Turn the power OFF.
METHOD #3
ALIGNMENT OF RATIO DETECTOR USING A
SWEEP GENERATOR AND OSCILLOSCOPE
Connect the sweep generator and oscilloscope to the
circuit as shown in Figure 32. Set the sweep generator
for 10.7MHz and minimum voltage out. Turn the power
ON and set the volume control to a minimum. Increase
the amplitude of the sweep generator until an “S” curve
is seen (refer to Figure 33). Using an alignment tool or
screwdriver, adjust the blue coil T5 until the “S” curve is
centered, until each half of the “S” is equal. Now adjust
the pink coil T4 for maximum “S” amplitude. Repeat
these steps until the alignment is optimized. Turn the
power OFF.
The purpose of the 2nd IF amplifier is to increase the
amplitude of the intermediate frequency (IF) while also
providing Selectivity. Selectivity is the ability to “pick
out” one station while rejecting all others. T3 acts as a
bandpass filter that only passes signals around
10.7MHz. The resistor R19 is used to widen the 3dB bandwidth of the 2nd FM IF amplifier.
The gain at 10.7MHz is fixed by the AC impedance of
the primary side of T3 and the current in Q5. The
current is fixed by R16, R17 and R18. Capacitors C18
and C17 bypass the AC signal to ground. C20 is a
bypass capacitor from V+ to ground.
Figure 33
SECOND FM IF AMPLIFIER