2. Assume that the power switch for the radio is in the ON position, and that th
ID: 2085723 • Letter: 2
Question
2. Assume that the power switch for the radio is in the ON position, and that the battery is in good condition. A voltmeter placed at the junction of R4 and D2 displays a reading of 1.5 V. What should the voltmeter read from the anode of D1 to ground?
3. There are seven capacitors in the AM radio circuit—C1, C2, C3, C4, C5, C6, and C7 . Of these seven capacitors, list four that have no effect on the tuning of the radio.
4. In which direction would the wiper arm of R3 have to be moved to increase volume?
5. In the construction of an electronic circuit, using a circuit board instead of point-to-point wiring provides several advantages. List three of the advantages of the printed circuit board.
6. In the AM radio circuit, which two components form the tuning network?
7. In the AM radio circuit, list four of the six components that form the AM tuner.
8. In the AM radio circuit, which capacitor decouples the tuner output?
9. In the AM radio circuit, which component controls the volume, and which component couples the tuner’s audio output signal to the volume control?
10. In the AM radio circuit, which component is the power audio amp?
Explanation / Answer
2)In some circuits negative is the same as ground, but in some circuits ground = 0 volts and in other parts of the circuit there is a negative voltage that is below ground. If you connect a voltmeter between ground (0 volts) and -1.5 volts it will read a difference of 1.5 volts, with the ground being most positive. Electrical parts work because of a difference in potiential.
3) C1 and C3 or C2 andC4)If a frequency counter is available then the chore will be super easy. If not, some experimenting with different pairs of capacitors (C1 and C3 or C2 and C4) will be necessary to bring both oscillators to the same frequency.
4)Wiper systems generally use two wipe speeds to suit the driving conditions and also an intermittent wipe facility is incorporated.To achieve this arrangement the circuit is switched-on so that the current through the armature is reversed after the motor has stopped. This charges the polarity of the brush in the permanent magnet motor so that the armature rotates in the opposite direction.
5) Thin size allows close packing of multiple boards or low profile products.
• Very consistent electrical properties reduces circuit variation and improves overall quality
• High electrical properties allows for high performance and consistent performance circuits
• Overall high quality and reliability
• Ease of inspection
6) L-C(inductor and capacitor) are the tuning components .
7) The combination of C1 and L1 comprise a resonant circuit, refered to as a tank circuit. Its purpose is to select one out of many available radios signals. The variable capacitor C1 allows for tuning to the various signals.
8)The decoupling capacitor at position (G) removes the radio frequencies by passing them to ground. The audio information signal remains and goes to the headphones.
9)10K preset VR controls the volume to the input of the amplifier. IC1 is the micro power audio amplifier that works between 4.5 to 12 volts DC. The amplified sound can be heard through the low impedance head phone or small Mylar speakers.
10)The LM2876 is a high-performance audio power amplifier capable of delivering 40W of continuous 8 average power to an 8 load with 0.1% THD+N from from 20Hz–20kHz.
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