Noise Figure is the correct answer.

Noise Figure refers to the amount of noise added by an amplifier to the input signal. In the context of a small-signal amplifier used in a radio receiver, measuring the Noise Figure is crucial to evaluate the amplifier's performance in terms of its ability to amplify weak signals while minimizing the introduction of additional noise.

Why is Noise Figure important in a radio receiver?

A radio receiver is designed to receive and amplify weak signals from various sources, such as radio stations or wireless communication devices. These weak signals are often accompanied by noise, which can degrade the quality of the received signal. Therefore, it is essential to measure and optimize the Noise Figure of the amplifier in the receiver to ensure that the desired signals are amplified while minimizing the impact of noise.

Understanding Noise Figure:

Noise Figure is defined as the ratio of the output noise power of the amplifier to the input noise power. It is usually expressed in decibels (dB). A lower Noise Figure indicates a better performance of the amplifier in terms of noise contribution.

The Noise Figure takes into account both the inherent noise of the amplifier itself and the noise contributed by the source impedance and the subsequent stages of the receiver. By measuring the Noise Figure, one can evaluate the overall noise performance of the receiver system.

Importance of measuring Noise Figure:

1. Sensitivity: The Noise Figure directly impacts the sensitivity of the receiver. A lower Noise Figure allows the receiver to detect and amplify weaker signals, improving its ability to receive signals in low signal-to-noise ratio conditions.

2. Signal Quality: The Noise Figure affects the signal quality by determining the signal-to-noise ratio. A higher Noise Figure introduces more noise, resulting in a lower signal-to-noise ratio and potentially degrading the quality of the received signal.

3. System Design: Measuring the Noise Figure helps in optimizing the design of the receiver system. It allows engineers to identify and address sources of noise, such as component selection, grounding, shielding, and filtering techniques, to improve the overall performance of the receiver.

In conclusion, when measuring the characteristics of a small-signal amplifier in a radio receiver, the Noise Figure is an important parameter to evaluate its noise performance. It helps in determining the sensitivity, signal quality, and overall design optimization of the receiver system.