The paper carried out the reasoning of the formula which implies the relationship between optical modulation depth and the input level of a optical transmitter and the formula implied between single channel modulation depth and bestir level & bias current.

In the essay narrate how to use the amplifier of cable TV correctly from five aspects: the character and kinds of amplifier, the transmission character of coaxial cable and taps to the TV signal, the smallest input level, the output level of amplifier and the points for attention of using amplifier.

During the designing and debugging of traditional CATV distribution amplifiers,a wide range of input levels and output levels have to be applied due to the limitation of distortion index,which is disadvantageous to improve the distribution efficiency and C/N index of the amplifier.

In this article,we analyze the reason why traditional designing method for amplifier does not fit the application environment nowadays,and present the evolution of the calculation formula for the output level of CATV amplifier.

Through concrete analyze, this paper points out the relation between C/N and each output level.

In the essay narrate how to use the amplifier of cable TV correctly from five aspects: the character and kinds of amplifier, the transmission character of coaxial cable and taps to the TV signal, the smallest input level, the output level of amplifier and the points for attention of using amplifier.