Blaupunkt-werke Gmbh

Hans Rasehorn

Wilhelm Hegeler

Jens Hansen

Lambert Maschmeyer

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

Frequencies which respectively identify a particular transmitter, and a particular program content, and which are in a very low frequency range (from between 20 to 125 kHz can be recognized, and ditigal output control signals derived representative of whether one, or both, or none of these frequencies are present by use of a frequency selection input circuit, controlled by a change-over switch to initially select recognition of the transmitter identification which, if positive, is applied through a storage circuit having a storage time substantially longer than the switch-over rate, to provide an output signal if the selected transmitter is recognized, and hold that output signal during switch-over of the program content identification signal which, if present, will be fed back through a logic circuit to hold the output of the transmitter identification circuit as identified, and if not present, permit continued switch-over of the frequency identification circuit to continue to store transmitter identification signals, if present, but permit these signals to disappear, after the storage time, if the transmitter identification signals also cease. The time delay and storage circuit preferably include operational amplifiers, and the frequency identification circuit includes a phase-locked loop.

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Hildesheim, Germany

Hans Rasehorn