Abstract: A transmitter encoder has a gain selector for compressing the level of a horizontal sync signal component of a video intermediate frequency (IF) signal to scramble it, and an AM modulation degree controller for superposing a control signal, which indicates the timing for the level compression, on an FM audio IF signal in the form of AM modulation. The transmitter encoder further has an oscillator circuit for generating a sine wave with a horizontal frequency (fH) and an nfH sine wave having a frequency n times the horizontal frequency, and a mixer for mixing these sine waves to thereby provide the above control signal. A receiver decoder has an AM detector for detecting an AM component of the FM audio IF signal from the transmitter encoder to reproduce a composite signal and band filters for respectively extracting the fH and nfH sine waves from the reproduced composite signal.

Abstract: An intermediate-frequency automatic gain control circuit generates an IFAGC voltage for controlling the gain of an IF amplifier, in accordance with the level of the output signal of the IF amplifier. An RFAGC voltage provides a voltage for controlling the gain of an RF amplifier of a tuner, in accordance with the IFAGC voltage level. The output voltage of the RFAGC circuit is supplied to a time-constant circuit made up of a series circuit including first and second resistors and a first capacitor, and a second capacitor connected in parallel with the series circuit. The time-constant circuit is connected to a time-constant control circuit made up of first and second diodes connected in parallel with the second resistor. When the output voltage level of the RFAGC circuit increases or decreases above or below the diode voltage, the first or second diode is conductive, to decrease the time constant of the time constant circuit.

Abstract: A CPU in a subscriber terminal generates upstream data and a transmission request signal as an enable signal for sending the upstream data to a broadcast center. An oscillator generates a carrier wave while the enable signal is being held at a predetermined level. A multiplier multiplies the carrier wave with the upstream data and generates the upstream signal. A transmission level adjusting amplifier amplifies the upstream signal, and the amplified signal is sent onto a cable. A detecting means receives a signal associated with the enable signal and discriminates the presence of the carrier wave. A time constant circuit measures the period of time for which the carrier wave is present in response to output from the detecting means. A switching circuit stops supplying at least the carrier wave of a first frequency onto the cable in response to output from the time constant circuit which indicates that the carrier wave has been exceeded the predetermined period of time.

Abstract: A video picture signal scrambling system for subscription braodcast or cablecast television systems which can scramble video signals without adversely effecting pictures received at a subscriber's terminal. The system includes a detector for detecting the brightness level of the picture signal over a predetermined interval, a comparator for comparing the brightness level with a first predetermined reference value and a scrambling circuit responsive to the comparator for inhibiting reversion of the picture signal when the brightness level exceeds the first reference value, and for selectively reversing the picture signal in response to changes in the brightness level in successive intervals of the picture signal.

Abstract: A cable television system includes security means. A security sensor is provided a subscriber's house and when it generates an emergency signal a transmission path is formed by non-active elements from the security sensor to a trunk cable. An external control unit has a checking function of a power supplying state to the security sensor. The external control unit can communicate with a central station with respect to power source conditions of subscribers.

Abstract: An external control unit for a CATV system has a CPU and a RAM with many kinds of memory maps. Reference data to be stored in the memory maps is transmitted from a central station. When a subscriber requests the tuning of a TV channel for a pay program to a converter tuner, the CPU in the external control unit can work, using the reference data.

Abstract: A variable frequency oscillator includes a RAM which stores a frequency setting data and provides a frequency control data, a VCO circuit which provides an oscillation output having a frequency which is defined by the contents of the frequency control data, a reference oscillator which provides a reference signal having a given frequency and phase, a phase comparator which detects the phase difference between the reference signal and a comparison signal corresponding to the oscillation output, and a logic circuit which combines the frequency control data with a phase data and provides the frequency setting data. The phase comparator provides the phase data whose contents indicate +1 if the phase of the comparison signal is delayed from the phase of the reference signal, indicate -1 if the phase of the comparison signal is advanced to the phase of the reference signal, and indicate 0 if the phase of the comparison signal matches with the phase of the reference signal.

Abstract: A transmitting section periodically radiates a signal wave. A receiving section receives the signal wave radiated from the transmitting section and reflected from the monitored region to produce the received signal. A sampling circuit samples the output signal from the receiving section at given time intervals. A memory stores the output signal from the sampling circuit at the time of one period of transmission, and a judging circuit compares the output signal from the sampling circuit at each transmission with the signal previously stored in the memory to detect a change in a state of an object to be detected.

Abstract: In a channel selection system of a television receiver set using a frequency synthesizer system, the local oscillator output of a voltage controlled oscillator in a tuner is coupled to through a prescaler to a programmable frequency divider. To a frequency division ratio specification input terminal of the programmable frequency divider is coupled a frequency division ratio setting data from a frequency division ratio memory. When the broadcast wave frequency is deviated from a predetermined value due to the frequency division ratio setting data, a fine tuning data corresponding to the deviation and a direction specification data representing the direction of the deviation are memorized in a random-access memory (RAM). The fine tuning data read out from the RAM is coupled to a fine tuning signal generator where it is added to or subtracted from the frequency division ratio setting data prevailing in the programmable frequency divider.