SCA1
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42. Install C18, 220 uf electrolytic. Again, check that polarity!
43. Install C19, .1 uf disc [marked .1 or 104].
44 Install C20, .01 uf disc [marked .01 or 103 or 10nf].
45. Next we'll install U2, the LM 386 audio amplifier IC. Use care when
inserting the IC into the circuit board not to bend one of the pins so it does
not pass through the circuit board. Note also that one end of the IC is
marked by a dot, notch or band; this end must be oriented as shown on the
PC board layout diagram.
46. Install R13, 2 ohm [red-black-gold].
47. Install the battery snap terminal leads, making sure that the positive
(red) lead is inserted into the (+) hole on the PC board and the negative
(black) into the (-) hole.
48. The battery bracket may be attached in a variety of ways. A wire
jumper can be passed through the two holes on the PC board, then both
ends soldered on the underside of the board.
49. A note concerning capacitor C22. If this component is installed, the
audio gain will be significantly increased. This can, however, be too much of
a good thing and cause feedback or audio distortion depending on the
speaker used. It's recommended that you do not install the component
initially, but add it after your SCA decoder has been tested and verified that
all else is working correctly. When and if you choose to install C22, a 10 uf
electrolytic, be sure to observe the polarity. Follow the parts layout diagram
for component orientation.
CONGRATULATIONS
Your subcarrier decoder is completed! Take a minute to step back and have a
look at your work. If you have the patience, we suggest a short break. Then,
take a magnifying lens and a bright light and examine all your solder joints,
touching up any connection which appears less than perfect. Make sure all
excess leads have been trimmed, and that there's not one bent back flat against
the board, probably causing a short. Brush the solder side of the board with a
stiff brush to make sure that no loose wire trimmings or solder drippings (tsk
tsk) are lodged between connections.
SCA DECODER SETUP AND TESTING
Initially, the demodulator can be tested as follows :