| 摘要 |
Signal quality in a cable in a particular frequency range is monitored and analyzed without interfering with the cable reception of CATV signals. Carrier signals at a transmitter are modulated with a pair of pass signals separated in time by a television frame period. Preferably before the first pass signal in the pair, a series of digital signals is provided indicating the parameters of a frequency sweep which is initiated upon the occurrence of the second pass signal. These parameters include the sweep start frequency, the sweep frequency bandwidth, the sweep duration and the sweep repetition rate. A frequency sweep according to such parameters is produced when the second pass signal occurs. The modulated carrier signals are transmitted through the cable to a receiver coupled to the cable. The receiver demodulates the carrier signals and processes the series of digital signals to determine the sweep signal parameters. When the first pass signal occurs, the CATV television signals in the cable pass to the receiver. When the second pass signal occurs, the television signals in the next cable frame also pass to the receiver for subtraction from the first CATV signals. Since these two signals are substantially the same, they are canceled. When the second pass signal occurs, the receiver receives the frequency sweep from the transmitter. These signals are stored in a digital memory for recirculation to a display. In this way, the quality of a transmission medium is determined and displayed without affecting the television signal quality in the medium.
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