Key Topic 42: RF Amplifiers

Question 1

3-42F1: How can selectivity be achieved in the front-end circuitry of a communications receiver?

A. By using an audio filter.
B. By using an additional RF amplifier stage.
C. By using an additional IF amplifier stage.
D. By using a preselector.

Answer 1

B. By using an additional RF amplifier stage.

Question 2

3-42F2: What is the primary purpose of an RF amplifier in a receiver?

A. To provide most of the receiver gain.
B. To vary the receiver image rejection by utilizing the AGC.
C. To improve the receiver’s nose figure.
D. To develop the AGC voltage.

Answer 2

C. To improve the receiver’s nose figure.

Question 3

3-42F3: How much gain should be used in the RF amplifier stage of a receiver?

A. Sufficient gain to allow weak signals to overcome noise generated in the first mixer stage.
B. As much gain as possible short of self oscillation.
C. Sufficient gain to keep weak signals below the noise of the first mixer stage.
D. It depends on the amplification factor of the first IF stage.

Answer 3

A. Sufficient gain to allow weak signals to overcome noise generated in the first mixer stage.

Question 4

3-42F4: Too much gain in a VHF receiver front end could result in this:

A. Local signals become weaker.
B. Difficult to match receiver impedances.
C. Dramatic increase in receiver current.
D. Susceptibility of intermodulation interference from nearby transmitters.

Answer 4

D. Susceptibility of intermodulation interference from nearby transmitters.

Question 5

3-42F5: What is the advantage of a GaAsFET preamplifier in a modern VHF radio receiver?

A. Increased selectivity and flat gain.
B. Low gain but high selectivity.
C. High gain and low noise floor.
D. High gain with high noise floor.

Answer 5

C. High gain and low noise floor.

Question 6

3-42F6: In what stage of a VHF receiver would a low noise amplifier be most advantageous?

A. IF stage.
B. Front end RF stage.
C. Audio stage.
D. Power supply.

Answer 6

B. Front end RF stage.