Abstract: In order to correctly perform frequency conversion without using a pilot signal from an external system in a CATV system in which an upward signal is converted to a high frequency in-building upward signal using an up-converter and the in-building upward signal is converted to the original upward signal using a down-converter, there is proposed a down-converter provided with a reference oscillation circuit for generating a reference signal with a frequency lower than that of a downward signal or the in-building upward signal. The in-building upward signal is frequency-converted using the reference signal and the reference signal is transmitted to a transmission line of the terminal side. A bi-directional amplifier on the transmission line can not only amplify the downward signal and the in-building upward signal bi-directionally but also transmit the reference signal to an up-converter of the terminal side.

Abstract: A down-converter comprises a frequency division circuit, PLL, and local oscillation circuit to convert a signal from a reference oscillation circuit to a converting reference signal with a constant frequency, and uses this signal to frequency-convert an in-building upward signal to an upward signal able to be transmitted in an external bi-directional CATV system. When the frequency of the converting reference signal deviates from the frequency of the converting reference signal on the side of an up-converter for converting the upward signal to the in-building upward signal on a terminal side, the upward signal cannot be accurately restored. Therefore, the down-converter uses the frequency division circuit to convert the converting reference signal to a transmitting reference signal with a low frequency, and outputs the transmitting reference signal to the terminal side.

Abstract: An in-building CATV system having a down-converter for converting the in-building upward signal to the signal for a bi-directional CATV system provided with a high-pass filter disposed between an internal terminal and a converter for eliminating input of the downward signal passed through the downward signal path and selectively passing the in-building upward signal, a low-pass filter disposed between the converter and an external terminal for eliminating the downward signal inputted from the external terminal and selectively passing the upward signal outputted from the converter, a high-pass filter disposed between the external terminal and the downward signal path for eliminating input of the upward signal outputted from the converter and selectively passing the downward signal inputted from the external terminal and a low-pass filter disposed between the downward signal path and the internal-terminal for eliminating the in-building upward signal inputted from the internal terminal and selectively passing t