A test system for measuring a frequency response between a first test point and a second test point of a cable television (CATV) network comprising:
- a head end for generating and receiving modulated digital signals, wherein each said digital signal occupies a pre-defined frequency band;
- and a cable plant for propagating said modulated digital signals;
- wherein the test system comprises:
- a cable modem operationally coupled to the first test point, for generating and receiving modulated digital signals;
- an injector operationally coupled to the first test point, for injecting, during a transmission time slot allocated by the head end for the modem to transmit a signal to the head end, a test signal having an amplitude and a test frequency, and for suppressing said test signal during a time that is outside of the transmission time slot, wherein:
- the frequency of the test signal to be injected is within a target frequency band, wherein the target frequency band is one of the pre-defined frequency bands, and a bandwidth of the test signal is sufficiently narrow so as not to impair reception of a modulated digital signal occupying said target frequency band, wherein said modulated digital signal is a target signal;
- the amplitude of the test signal to be injected is sufficiently low so as not to impair reception of said target signal;
- and
- the amplitude of the test signal to be injected is sufficiently high so as to be measurable at the second test point;
- an injector controller operationally coupled to the modem and to the injector, for receiving a digital signal from the cable modem and for controlling, in dependence upon said received digital signal, values of the amplitude and the frequency of the test signal to be injected during the transmission time slot;
- a selector operationally coupled to the second test point, for suppressing the target signal and selecting the test signal at the test frequency during a reception time slot that is delayed relative to the transmission time slot by a time of propagation of the test signal between the first and the second test points of the CATV network;
- a detector operationally coupled to the selector, for receiving the selected test signal from the selector and for measuring the amplitude of the selected test signal during the reception time slot;
- wherein either detector or selector, or both, comprise a circuit for suppressing all signals during a time that is outside of the reception time slot;
- a communication device operationally coupled to the second test point, for generating and receiving modulated digital signals;
- and
- a processor operationally coupled to the communication device, to the selector, and to the detector,
- for communicating to the injector controller the values of the amplitude and, or the frequency of the test signal to be injected, by causing the communication device to send a corresponding modulated digital signal through the CATV network;
- for communicating the value of the frequency of the test signal to the selector;
- for obtaining the measured amplitude of the received test signal from the detector;
- and
- for dividing the measured amplitude by the injected amplitude of the test signal, so as to obtain the frequency response of the CATV network between the first and the second test points, at the frequency of the test signal.