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FR-220
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6
The MC3359 IC has an internal oscillator controlled by the 10.245 MHz
crystal. The 10.245 MHz signal is mixed with the 10.7 MHz input from U1
to convert down to the low IF of 455 KHz. The 455 KHz IF is filtered by
FL2 and then amplified by a limiting amplifier in U2. Audio demodulation
takes place in the quadrature detector, with L4 adjusting the detector.
The audio modulation is detected in U2, and the background noise is
used to control the squelch. U3 amplifies the audio output from pin 10 of
U2 to a practical level for speaker or headphone operation. Pin 16 of U2
will ground the input of U3 when the squelch is closed.
L4, a 455 KHz IF coil, permits adjustment of the 90-degree voltage-
current phasing ("quadrature") of FL2's output to the FM detector
demodulator (pin 8 of the MC3359).
PARTS LIST
Inductors
❒
2 small 4 turn coils (L1,L2)
❒
1 slug-tuned 3È turn coil (L3)
❒
1 shielded transformer coil marked LB 53303 HK (L4)
Semiconductors and IC's
❒
1 2SC2570A or 2SC2498 transistor (Q1)
❒
3 2N3904 transistor (Q2,Q3,Q4)
❒
1 SA602 8-pin IC (U1)
❒
1 MC3359 18-pin FM receiver IC (U2)
❒
1 LM386 8-pin audio amplifier IC (U3)
❒
1 Varactor diode, BB405 [small black body with white band] (D1)
❒
1 1N914/1N4148 signal diode (D2)
Special Components
❒
1 10.245 MHz Crystal (Y1)
❒
1 10.7 MHz ceramic filter [brown, molded, 3 leads] (FL1)
❒
1 455 KHz ceramic filter [black, square] (FL2)
Содержание FR220
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