Tuned Amplifiers Interview Questions and Answers:

1. What is a tuned amplifier?

Ans. The amplifier used for amplifying a signal of specific frequency or narrowband of frequencies is known as a tuned amplifier.

2. What is the fundamental difference between audio amplifiers and tuned amplifiers?

Ans. The fundamental difference between audio amplifiers and tuned amplifiers is the bandwidth they are expected to amplify. Audio amplifiers amplify a major portion of audio-frequency spectrum (20 Hz-20 kHz) equally well throughout while tuned amplifiers amplify a relatively narrow portion of RF spectrum, rejecting all other frequencies.

3. Give the typical value of Q of a coil used in class C tuned amplifiers.

Ans. 50 or more.

4. What is the typical value of Q for the circuit of a class C tuned amplifier?

Ans. 10 or more.

5. Why the quality factor of the whole circuit is less than that of the inductor?

Ans. The quality factor Q for the whole circuit is less than that of the inductor because it includes the effect of load resistance as well as the coil resistance.

6. Tuned-class C amplifiers are used for applications involving larger RF power. Why?

Ans. Tuned amplifiers operating in class A operation are not suitable for applications involving large RF power, because of lower efficiency of class A operation. For applications involving larger RF power, like for excitation of transmitting antenna, tuned class C amplifiers are employed because class C operation has a very high efficiency and is capable of delivering more power in comparison to that of class A operation.

7. Define stagger tunning.

Ans. A much better overall response can be had by stagger-tuning the individual stages. Stagger tuned amplifiers are usually designed so that the overall response exhibits maximal flatness around the centre frequency f₀. It needs a number of tuned circuits operating in union. The overall frequency response of a stagger tuned amplifier is obtained by adding the individual response together. Since the resonant frequencies of different tuned circuits are displaced or staggered, they are referred to as stagger tuned amplifier. The main advantage of stagger tuned amplifier is increased bandwidth. Its drawbacks are reduced selectivity and critical tuning of many tank circuits. They are used in RF amplifier stage in radio receivers.

8. Justify the name of stagger tuned amplifiers.

Ans. Since the resonant frequencies of different tuned circuits used in stagger tuned amplifiers are displaced or staggered, they are referred to as stagger tuned amplifiers.

9. What is the advantage of stagger tuned amplifier?

Ans. Stagger tuning results in increased bandwidth.

10. What are the drawbacks of stagger tuned amplifiers?

Ans. The drawbacks of stagger tuned amplifiers are:

• Reduced selectivity.
• Tuning of many tank (L-C) circuits precisely at different frequencies is quite cumbersome.

11. Give the application of stagger tuned amplifiers.

Ans. Stagger tuned amplifiers are used in RF amplifier stage in radio receivers.