Bidirectional trunk amplifier and cable modem for cable hybrid fiber and coax network which utilizes an upstream pilot signal

A cable modem for bidirectional services in an HFC (Hybrid Fiber and Coax) network, comprising:

• a central processing unit (CPU);
• a tuner for downconverting upconverted downstream signals into IF (Intermediate Frequency) signals having constant frequency, by utilizing RF (Radio Frequency) signals;
• a saw filter for filtering a specified band frequency of the IF signals received from the tuner;
• a mixer and AGC (Automatic Gain Controller) for converting the filtered IF signals into base band signals and for outputting a gain control signal;
• a LPF (Low Pass Filter) for passing only low band signals and removing high band signals from the signals generated by the mixer and AGC;
• a gain controller for controlling the level of the signals received from the mixer and AGC so that the level of the signals output by the mixer and AGC is constant;
• a downstream demodulator for recovering and converting the base band signals from the LPF into pre-modulated digital signals by demodulating the modulated signals;
• a MAC (Media Access Controller) for dividing the demodulated signals into control signals and data signals and for transmitting upstream data signals to the transceiver under the control of the CPU;
• an upstream modulator for modulating the upstream data signals received from the MAC to be transmitted to the headend;
• a programmable attenuator for controlling the level of the modulated upstream signals;
• a pilot signal generator for generating a pilot signal;
• and
• a switch for connecting said tuner and said pilot signal generator under the control of the CPU.