Blaupunkt-Werke Gmbh

Jens Hansen

Willy Minner

Hans Rasehorn

Thomas Schafer

Tape segment identifying signals in a frequency range below the lower threshold of sound signals that can be recorded or played back from the tape are recorded on the sound track of a video tape, a characteristic such as the frequency, pulse length, or phase of the identifying signals being changed stepwise as successive tape segments corresponding to successive scenes or successive periods of playing time are recorded. To find a selected segment for playback, beginning when the tape is in any position in the machine, the tape transport mechanism is put into the fast-forward or reverse mode, the identifying signals are filtered by a low-pass filter having a cutoff frequency dependent upon tape speed and then are passed through a pulse-shaping circuit to produce square waves, after which the frequency, pulse length or phase is digitally measured and compared with a selected value representing the segment to be found, using synchronizing pulses, such as the vertical synchronizing pulses of a television signal, as reference signals. The detection circuit is so coordinated with the direction of tape transport as to produce a 'match' signal at the beginning of the tape segment selected, which signal puts the equipment in readiness for playback.

Magnetic tape reproducer-recorder with means for tape segment

A signal being received and superimposed disturbance pulses are taken from a stage of the receiver where the signal is a periodic wave of constant amplitude or of amplitude varying at rates limited by a moderate modulation band, and the signal so picked up is AC-coupled to a diode clamp circuit, the clamp voltage then being amplified to produce a control output for a blanking gate. The forward voltage of the diode is insufficient to put the transistor of the following amplifier into its conducting condition, so that the transistor conducts only when a disturbance pulse extends beyond the limits of the envelope of the sinusoidal signal. By the use of a phase splitter, two identical clamp circuits may be operated to detect disturbance pulses of opposite polarity, and their outputs may be combined to provide blanking control pulses whenever a disturbance pulse of either polarity appears.

Disturbing signal detection circuit

A circuit resonant at a frequency above the frequency band occupied by a signal to be protected is set into damped oscillations by high-frequency components of an interfering pulse and produces a voltage spike at the beginning of the interfering pulse. A differentiator circuit produces a close succession of a pair of oppositely polarized spikes in response to the spike produced by the resonant circuit, while substantially eliminating the rest of the signal and a switching transistor is caused to discharge a capacitor suddenly when the positive-going spike of the pair reaches it. The common connection point of the coil, capacitor and resistor of the resonant circuit is a point at which a delayed signal is obtained and the signal to be protected is thus provided with the benefit of this delay before it is subjected to blanking by the pulse produced at the collector of the switching transistor.

Interference pulse detector circuit

Radio frequency disturbance recognition circuits having their inputs tuned to different frequency bands by resonant circuits are coupled to the antenna input of a receiver to be protected through a decoupling stage that prevents excessive coupling and AND-gates are provided so that an interference blanking circuit will be operated to produce a momentary interruption of the low-frequency signal path only when a disturbance is detected by the radio frequency recognition circuits in both of their respective operating frequency ranges and at the same time a pulse disturbance is detected in the output of the receiver demodulator by a disturbance voltage detector circuit tuned to a frequency band higher than the frequency band of the low-frequency signal to be protected.

Interference pulse suppression circuit for radio receivers

A pulse amplifier with its input across the power supply leads to an automobile radio receiver to be protected against pulse interference is used to operate a blanking gate interposed between the demodulator of the receiver and the low-frequency circuits thereof. One of the power supply leads is grounded to the vehicle body. A resistor in the ungrounded lead increases the sensitivity of the pulse interference suppression circuit without impairing receiver operation. The circuit provides interference suppression that is not dependent upon the receiver band width and therefore usable both for AM reception and for FM reception.

Interference suppression circuit for automobile radio receivers

RC low-pass and high-pass filters are fed in common with a demodulated broadcast signal through a noise blanking switch device and the outputs of the respective filters are added in a summing amplifier, of which the output is supplied to the low-frequency stages of the receiver. For stereo reception, the crossover between the filters is made lower than the lowest pilot frequency of the composite demodulated signal, so that the circuit functions as an all-pass filter in the absence of disturbances and stores only the audible frequency program signal for transmission to the low-frequency stages during blanking intervals. For purely monophonic receivers, the passbands of the two filters may be spaced apart in frequency so as to provide a dip in the sum characteristic in the transition region contributing high-frequency de-emphasis to the audible signal, while still allowing transmission of an inaudible pilot signal or other superposed demodulated signal above the audible range when there is no interference blanking taking place.

Circuit for storing the amplitude of the lower-frequency portion of a

Two disturbance recognition circuits are supplied in parallel with the output of the receiver demodulator, one of them having a threshold characteristic with a sensitivity maximum only slightly above the frequency band of the received signal and a steep sensitivity frequency characteristic between that maximum and the upper edge of the signal band, while the other recognition circuit has its sensitivity well above the main sensitivity range of the first-mentioned recognition circuit. An AND-circuit is provided at the ouputs of the recognition circuits so that a blanking pulse will be produced only when both recognition circuits respond. The output pulse of the recognition circuit with the higher frequency sensitivity is broadened so that it will persist in the AND-circuit long enough to allow for the slower response time of the other recognition circuit. Blanking is disabled by a parallel switch when the rate of operation of the AND-circuit reaches a rate at which audible effects would be produced anyway.

Disturbance pulse detector circuit for radio receiver blanking

A frequency sensitive network responsive to frequencies somewhat above the useful signal band of a demodulated radio signal is interconnected with the inputs of a differential amplifier, so that the desired signal and the portions of the interference signals unaffected by the frequency sensitive circuit cancel out and a 'stripped' interference signal is obtained which is fed to a transistor circuit that produces trigger pulses for a multivibrator, regardless of which side of the differential amplifier first produces a pulse. The multivibrator provides pulses to a blanking switch and also charges a capacitor in a RC network, in which charge accumulates when the control pulses are bunched closely in time and this effect is used to produce a bias for disabling the provision of trigger pulses to the multivibrator until the capacitor charge leaks off.

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Hildesheim, Germany

Jens Hansen