The input level signal to an Amplifier is of crucial importance to the noise performance. Low level signals deteriorate rapidly with the injection of noise. On the other hand noise contributed to high level signals plays a less significant role. Given this basic understanding, a good starting point is to always ensure that input level signals are maintained fairly high for each Amplifier. An input signal level of atleast 65 dBU, preferably 70 dBU should be maintained at the input of each Amplifier, throughout the entire Cable TV network.
Lets take a closer look.
To start with, we need to estimate the noise performance of a single Amplifier. Once this noise is estimated, it would be a relatively simple matter to estimate the overall noise performance of the cascade of similar Amplifiers on the network. Keep in mind that we need to estimate the noise performance of the cascade of Amplifiers i.e. the chain of Amplifiers where the output of one feeds the other. Let us assume that a Cable TV network has 3 trunk lines. The network therefore has a total of 29 Amplifiers but the worse noise will be at the end of trunk 2 which has 12 Amplifiers in cascade.