DETAILED DESCRIPTION One object of the present invention, in a bi-directional CATV system, not only transmitting a downward signal and an upward L signal, with a frequency lower than the frequency of the downward signal, but also transmitting an upward H signal with a frequency higher than the frequency of the downward signal, is to reduce the transmission losses of the upward H signal at a CATV amplifier so that the CN ratio and the distortion due to the hum modulation in the entire system can be improved.
In order to attain the above object, a first aspect of this invention provides a CATV amplifier in which, out of the transmission signals flowing through the transmission line of a bi-directional CATV system, the downward signal, input to a first terminal from the transmission line on the center equipment side, is input to a downward amplifying circuit via a first filter and a second filter.
The upward L signal, input from the transmission line on the terminal device side to a second terminal, is input to an upward L amplifying circuit via the first filter and a third filter.
And the upward H signal, also input from the transmission line on the terminal device side to the second terminal, is input to an upward H amplifying circuit via a fourth filter.
Additionally, in the signals amplified at each of the amplifying circuits, the downward signal, amplified at the downward amplifying circuit, is transmitted to the transmission line on the terminal device side via the second filter, the first filter, and the second terminal.
The upward L signal, amplified at the upward L amplifying circuit, is transmitted to the transmission line on the center equipment side via the third filter, the first filter, and the first terminal.
And the upward H signal, amplified at the upward H amplifying circuit, is transmitted to the transmission line on the center equipment side via the fourth filter and the first terminal.
According to a CATV amplifier of the present invention for the three types of transmission signals flowing through the transmission line of the bi-directional CATV system, the upward H signals, of which the transmission losses in the transmission line grow the most significantly, only pass through the fourth filters provided in the former and latter stages of the upward H amplifying circuit
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