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close this bookRadio and Electronics
View the document(introduction...)
Open this folder and view contents1. INTRODUCTION
Open this folder and view contents2. PRINCIPLES OF RADIO COMMUNICATION UNICATION
Open this folder and view contents3. TRANSDUCERS
Open this folder and view contents4. RADIOWAVES
Open this folder and view contents5. MODULATION OF RADIOWAVES
Open this folder and view contents6. RECEPTION OF RADIOSIGNALS (AM - TYPE)
Open this folder and view contents7. COMPONENTS OF MODERN RADIO RECEIVERS
Open this folder and view contents8. PASSIVE COMPONENTS
Open this folder and view contents9. ACTIVE COMPONENTS -1- DIODES
Open this folder and view contents10. BLOCKS OF RADIOS / -1- / POWER SUPPLIES
Open this folder and view contents11. ACTIVE COMPONENTS -2- / TRANSISTORS
Open this folder and view contents12. AMPLIFIERS
Open this folder and view contents13. CLASS B AMPLIFIERS
View the document14. DETECTOR OR DEMODULATOR
View the document15. AGC-AUTOMATIC GAIN CONTROL
View the document16. IF-AMPLIFIERS
View the document17. FEEDBACK
View the document18. OSCILLATORS
View the document19. FREQUENCY CHANGERS MIXERSTAGE
View the document20. DECOUPLING CIRCUITS
View the document21. MATCHING OF AMPLIFIERSTAGES
View the document22. COUPLING OF AMPLIFIERSTAGES
Open this folder and view contents23. RADIO SERVICING
View the document24. THE USE OF THE OSCILLOSCOPE

22. COUPLING OF AMPLIFIERSTAGES

GENERAL REMARK

Amplifierstages have a HIGH INPUT IMPEDANCE while they have on the other hand A RATHER LOW OUTPUT IMPEDANCE. As explained during the chapter MATCHING this causes problems if we want to secure an efficient coupling.

COUPLING BY TRANSFORMERS

The most effective way to couple two amplifier stages for ac-signals is to couple them by a transformer.

In this case it is easily possible to use as a collector resistance of the first amplifier-stage which will deliver the signal the primary coil of the transformer. The secondary coil of the transformer is connected within the path from the biasing circuit to the base of the second.

An example is shown in fig. 206. By choosing the fitting number of turns it is possible to adjust the impedances of the two coils exactly to their complimentary impedances within the amplifierstages.


fig. 206

This method was used especially in the early days of transistor technology, when it was necessary to have as few transistors as possible (because of their high prices at that time).

Now you know all the different blocks of a simple AM-radio and you should be able to read the circuit diagram below.


figure

CHECK YOURSELF:

1. What does FEEDBACK mean?

2. What advantage has:

a) positive feedback
b) negative feedback?

3. What does “matching” mean?

4. Which type of coupling of amplifier-stages is the most accurate one?

5. Can you differentiate the blocks of the radio?

6. Explain what the components in the blocks are for!