Radio and Electronics (DED Philippinen, 66 p.): 3. TRANSDUCERS: 3.1. MICROPHONES

Radio and Electronics (DED Philippinen, 66 p.)

(introduction...)

1. INTRODUCTION

(introduction...)

1.1. A TRIAL TO STATE A DEFINITION OF ELECTRONICS

1.2. A SHORT HISTORY OF ELECTRONICS

1.3. CLASSIFICATION OF ELECTRONIC DEVICES

2. PRINCIPLES OF RADIO COMMUNICATION UNICATION

2.1. BASICAL IDEAS ABOUT COMMUNICATION

2.2. DEVELOPMENT OF LONG DISTANCE COMMUNICATION

2.3. FIDELITY AND DISTORTION

3. TRANSDUCERS

(introduction...)

3.1. MICROPHONES

3.2. LOUDSPEAKERS

3.3. THE TELEPHON SYSTEM

3.4. PROBLEM OF FREQUENCY RANGES

3.5. BANDWIDTH

4. RADIOWAVES

(introduction...)

4.1. ORIGIN OF RADIOWAVES

4.2. PARAMETERS OF ELECTROMAGNETIC WAVES

4.3. PROPAGATION OF RADIOWAVES

4.4. SPECTRUM OF RADIOWAVES AND BANDS OF RADIOWAVES

5. MODULATION OF RADIOWAVES

(introduction...)

5.1. THE AMPLITUDE MODULATION (AM)

5.2. FREQUENCY MODULATION (FM)

5.3. SIDEBANDS

5.4. TRANSMISSION OF RADIOSIGNALS

6. RECEPTION OF RADIOSIGNALS (AM - TYPE)

6.1. AERIAL

6.2. THE TUNED CIRCUIT

6.3. INCIDENTAL REMARK ON BLOCK DIAGRAMS

6.4. DETECTOR OR DEMODULATOR

6.5. POWER SUPPLY

6.6. AMPLIFIER

6.7. SUPERHET RECEIVER (the SUPER)

6.8 INCIDENTAL REMARK ON MIXING FREQUENCIES

6.9. CONSTRUCTION OF A SUPERHETRADIO

7. COMPONENTS OF MODERN RADIO RECEIVERS

7.1.1. HANDLING OF ELECTRONIC COMPONENTS

7.1.2. HANDLING OF PRINTED CIRCUITS

7.1.3. DIFFERENTIATION OF COMPONENTS

8. PASSIVE COMPONENTS

8.1. RESISTORS ELECTRICAL CHARACTERISTICS

8.2. CAPACITORS

8.3. INDUCTORS

8.4. COMBINATION OF PASSIVE COMPONENTS

8.4.1. SERIES CONNECTION OF R AND C, OR R AND L

8.4.2. COMBINATION OF L AND C, RESONANT (TUNED) CIRCUITS

8.4.3. TUNED CIRCUIT CONNECTED TO AN AC-VOLTAGE

(introduction...)

8.4.4.1. QUALITY OF TUNED CIRCUITS

8.4.4.2. BANDWIDTH

9. ACTIVE COMPONENTS -1- DIODES

9.1. CHARACTERISTICS OF SEMICONDUCTORS

9.2. THE PN-JUNCTION OR DIODE

(introduction...)

9.2.1. PN-JUNCTION CONNECTED TO VOLTAGE

9.2.2. CHARACTERISTICS OF A PN-JUNCTION OR DIODE

9.2.3. ZENERDIODE

10. BLOCKS OF RADIOS / -1- / POWER SUPPLIES

10.1. GENERAL CONSIDERATIONS

10.2. TRANSFORMER

10.3. THE RECTIFIERS.

10.4. SMOOTHING AND FILTER CIRCUITS

10.4.1. THE RESERVOIR CAPACITOR

10.4.2. FILTER CIRCUITS

10.5. STABILIZATION

10.5.1. GENERAL REMARKS

10.5.1.1. LOAD VARIATIONS

10.5.1.2. INTERNAL RESISTANCE OF VOLTAGESOURCES

10.5.1.3. PROBLEMS CAUSED BY THE SMOOTHING CIRCUIT

10.5.5. METHODS OF STABILIZATION

(introduction...)

10.5.5.1. PARALLEL-STABILIZATION

10.5.2.2. SERIES STABILIZATION

11. ACTIVE COMPONENTS -2- / TRANSISTORS

11.1. CONSTRUCTION OF A TRANSISTOR

11.2. CHARACTERISTICS OF TRANSISTORS

(introduction...)

11.2.1 HANDLING OF CHARACTERISTICS OF TRANSISTORS

11.2.1.1. CONSTRUCTION OF THE STATIC-MUTUAL-CHARACTERISTICS

11.2.1.2. CONSTRUCTION OF THE DYNAMIC MUTUAL CHARACTERISTICS

11.2.1.3. CONSTRUCTION OF THE MAXIMUM-POWER-LINE

12. AMPLIFIERS

(introduction...)

12.1. STRUCTURE OF A CLASS A AMPLIFIER

12.2. FUNCTION OF A SIMPLE CLASS A AMPLIFIER

12.3. ADVANCED CLASS A AMPLIFIER

12.4. STABILIZATION OF THE QUIESCENT VOLTAGE

13. CLASS B AMPLIFIERS

13.1. LIMITS OF CLASS A AMPLIFIERS

13.2. CLASS B AMPLIFIERS WITH TRANSFORMERS

13.3. CLASS B AMPLIFIERS WITHOUT TRANSFORMERS

13.4. POWER AMPLIFIER WITH COMPLIMENTARY TRANSISTORS.

14. DETECTOR OR DEMODULATOR

15. AGC-AUTOMATIC GAIN CONTROL

16. IF-AMPLIFIERS

17. FEEDBACK

18. OSCILLATORS

19. FREQUENCY CHANGERS MIXERSTAGE

20. DECOUPLING CIRCUITS

21. MATCHING OF AMPLIFIERSTAGES

22. COUPLING OF AMPLIFIERSTAGES

23. RADIO SERVICING

23.1. IMPORTANCE AND SUBJECT OF FAULT FINDING

23.2. FAULTS AND FAULT FINDING

23.3. FAULT FINDING METHODS

24. THE USE OF THE OSCILLOSCOPE

3.1. MICROPHONES

CARBON MICROPHON is a very old type but still in use when a cheap microphon is desired and fidelity is not so important. CARBON GRANULATES change their resistance, if they are pressed together by an external force. The inner hollow part of the microphon is filled with this type of carbon particles. At the front of the microphon is fixed a very thin sheet of metal which is here the diaphragm, and at the backside is fixed a second metalplate which stands here as an electrode to give contact to the carbon granulates.

When exposed to sound the diaphragm is moved by the air oscillations, and the pressure on the carbon granulates changes according to the frequency of the air-oscillations. Therefore the overall resistance of the carbon granulates changes according to the frequency of the sound.

fig. 9

ELECTROSTATIC MICROPHON

Is working like a variable capacitor. The diaphragm is made from metal and stands for one plate of the capacitor. It is positioned very near to a second metalsheet with a lot of holes in it a few tens of millimeter inside of the microphone. This second metalplate stands for the second plate of the capacitor. If the diaphragm is hit by soundwaves it moves to and for, and by doing so, the distance between the tow plates changes. As well know from physics, the change of the distances lets also change the capacity of the capacitor. So the whole microphone stands for a capacitor which changes its capacity according to the sound waves hitting the diaphragm.

fig. 10

ELECTRODYNAMIC MICROPHON

Here a coil is fixed to a diaphragm made from insulating material (like cardboard):

This coil is positioned free within the gaps of a strong permanent magnet.

If the diaphragm is moved by soundwaves, the coil is moving to and for as well.

This movement causes induction of a voltage in the coil and so this microphon is producing a voltage depending on the frequency of the sound waves.

fig. 11

CRYSTAL MICROPHON

Here is used the so-called PIEZO EFFECT. If a crystal is exerted to pressure there will appear a voltage across its edges. The force to press is produced again by diaphragms, now positioned in front and behind the crystal. If the diaphragms are moved to and for by air-pressures the microphone generates a low voltage which has the same frequency as the sound wave have it.

fig. 12