Which method minimizes the amount of thermal noise added to a network?

The method that minimizes the amount of thermal noise added to a network is ensuring that the RF input is above the minimum input level. This approach is effective because when the RF signal level is sufficiently high, it can overcome the thermal noise present in the system. Thermal noise, which is generated by the movement of electrons in conductors, is a significant factor in signal degradation at lower input levels. By ensuring that the RF input is above a certain threshold, the signal-to-noise ratio improves, significantly reducing the impact of thermal noise on signal quality.

In contrast, adding more amplifiers can sometimes introduce additional noise rather than mitigate it, particularly if they are not properly matched or if they operate near their noise figure limits. Lowering the operating frequency can impact system performance in different ways, particularly with respect to cable losses and return loss, but it does not directly reduce thermal noise generated in the components. Lastly, using longer cables tends to increase attenuation and can actually introduce more thermal noise due to the length and characteristics of the cable itself, leading to further degradation of the signal rather than improvement.