Abstract: In a Hybrid Fiber Coaxial (HFC) network using a Set Top Box (STB) or a cable modem, the cable STB or the cable modem includes respective High-Pass Filters (HPFs) having different passband frequencies to transmit an upstream signal from the cable STB or the cable modem to the HFC network through paths having different passband frequencies depending on states of the HFC network so that the upstream frequency band of 5 to 42 MHz is available.

Abstract: A cable modem includes a CPU for controlling the entire cable modem, a PGC, for generating a modem signal with adjusted intensity, a transformer for isolating the PGC from a next stage, a low pass filter for filtering off a high-frequency component, and a selecting circuit for selectively transferring the output signal form the low pass filter to a network. In particular, the cable modem of the invention is advantageous for preventing an up-stream signal of the cable modem from transferring to an HFC network and for preventing the entire network to be shut down when an internal circuit operates abnormally.

Abstract: In a Hybrid Fiber Coaxial (HFC) network using a Set Top Box (STB) or a cable modem, the cable STB or the cable modem includes respective High-Pass Filters (HPFs) having different passband frequencies to transmit an upstream signal from the cable STB or the cable modem to the HFC network through paths having different passband frequencies depending on states of the HFC network so that the upstream frequency band of 5 to 42 MHz is available.

Abstract: A cable modem includes a CPU for controlling the entire cable modem, a PGC, for generating a modem signal with adjusted intensity, a transformer for isolating the PGC from a next stage, a low pass filter for filtering off a high-frequency component, and a selecting circuit for selectively transferring the output signal form the low pass filter to a network. In particular, the cable modem of the invention is advantageous for preventing an up-stream signal of the cable modem from transferring to an HFC network and for preventing the entire network to be shut down when an internal circuit operates abnormally.

Abstract: A noise reducing apparatus for minimizing spurious noise in a system utilizing a cable modem is provided. The noise reducing apparatus for reducing a noise generated according to operation of a modem includes a controlling unit for controlling the modem and producing an enable signal according to generation of the noise, a programmable gain controller for turning on/off a transmission level in response to the enable signal of the controlling unit, a noise removing unit for removing predetermined noise generated by the programmable gain controller when the modem does not transmit a signal, and a tuner for tuning the output of the noise removing unit to connect it to a coaxial cable network. Since a circuit comprised of gates and gallium arsenide integrated circuit single-pole double-throw switches is employed therein to minimize spurious noise when a cable modem does not transmit a signal, the quality in the communication between a cable modem and a headend can be ensured.

Abstract: There is provided an ingress noise measuring device for each subscriber's terminal in a data communication network using a cable television (CATV) network. The ingress noise measuring device has a transformer connected between a cable MODEM and the CATV network, a switch connected between the transformer and the cable MODEM, and an RF radio-transmission unit for radio-transmitting an RF signal by switching. A display is connected to a contact point between the transformer and the subscriber's terminal, for visually displaying the strength of the RF signal received from the subscriber's terminal.