Abstract: A circuit is disclosed that includes a pair of varactors coupled to an input sample circuit and having an appropriate capacitance during the sample strobe of the input to minimize sampling errors. The varactors are combined with a control switch having an output timed to symmetrically reduce the capacitance to a new value, preferably a value approaching the input capacitance of a field effect transistor which is included in the output circuit. In this way, a noise-free voltage and power gain of CT0/CT1 can be reached, where CT0 is the initial value of the capacitance of the sampling circuit and CT1 is the final value of the capacitance of the sampling circuit.

Abstract: 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.