Abstract: A system for identifying a program stream being displayed at a receiver location comprises means at a central station for measuring the relative luminance of a plurality of predetermined areas in each frame and recording that data with their times of occurrence for each of a plurality of program streams as reference data, and means at a receiver location to measure the relative luminance of the same areas but at a repetition rate less than that at the central station for a given time after a channel change and thereafter at an even lower repetition rate and storing the measurements at the receiver location with times defining corresponding broadcast times, and means for transmitting the stored data to the central station for correlating the measured and reference data using the recorded times to access the corresponding measured values of the recorded and reference data.

Abstract: A fractional-N type frequency synthesizer has a voltage controlled oscillator controlled in a phase-locked loop by a divide by N divider and a phase comparator responsive to the divided frequency and to a reference frequency Fr. An accumulator is responsive to the desired fractional part of the N and is clocked by Fr to produce carry signals for producing the required periodic variations in N. A second accumulator produces periodic equal and opposite further variations in N to reduce the magnitude of the error waveform which would be given to the phase-detector output by the variations in n caused by the first accumulator. A digital to analog converter and a differentiating circuit produce a jitter correction signal for reducing residual jitter. A coherent detector detects for the presence of any residual jitter at the control input of the VCO and resulting from the fractional-N control circuit.

Abstract: An automatic gain control (AGC) circuit arrangement is disclosed as including an AGC loop responsive to an input signal and operative to maintain an output signal at a desired mean level represented by a reference signal applied in the loop and also subjected to amplitude modulation by an AF signal. The circuit arrangement includes modulators outside the loop for changing the level of the input signal by amounts corresponding respectively to changes in level represented by changes in the AF signal and by changes in the reference signal. Therefore, the level of the input signal as received by the AGC loop is at least approximately at the right value and its gain is held substantially constant even when the level of the required output signal for a given input signal changes. Therefore, variations of bandwidth resulting from gain variations are avoided.